diff --git a/features/fixtures/mazerunner/jvm-scenarios/detekt-baseline.xml b/features/fixtures/mazerunner/jvm-scenarios/detekt-baseline.xml
index 1fcda340f9..d18bb02cbd 100644
--- a/features/fixtures/mazerunner/jvm-scenarios/detekt-baseline.xml
+++ b/features/fixtures/mazerunner/jvm-scenarios/detekt-baseline.xml
@@ -24,6 +24,8 @@
     <ID>MagicNumber:StartupCrashFlushScenario.kt$StartupCrashFlushScenario$6000</ID>
     <ID>MagicNumber:TestHarnessHooks.kt$&lt;no name provided>$500</ID>
     <ID>MagicNumber:TrimmedStacktraceScenario.kt$TrimmedStacktraceScenario$100000</ID>
+    <ID>MagicNumber:UnhandledExceptionEventDetailChangeScenario.kt$UnhandledExceptionEventDetailChangeScenario$123</ID>
+    <ID>MagicNumber:UnhandledExceptionEventDetailChangeScenario.kt$UnhandledExceptionEventDetailChangeScenario$123456</ID>
     <ID>ThrowingExceptionsWithoutMessageOrCause:AnrHelper.kt$&lt;no name provided>$IllegalStateException()</ID>
     <ID>ThrowingExceptionsWithoutMessageOrCause:BugsnagInitScenario.kt$BugsnagInitScenario$RuntimeException()</ID>
     <ID>ThrowingExceptionsWithoutMessageOrCause:CustomPluginNotifierDescriptionScenario.kt$CustomPluginNotifierDescriptionScenario$RuntimeException()</ID>
diff --git a/features/fixtures/mazerunner/jvm-scenarios/src/main/java/com/bugsnag/android/mazerunner/scenarios/UnhandledExceptionEventDetailChangeScenario.kt b/features/fixtures/mazerunner/jvm-scenarios/src/main/java/com/bugsnag/android/mazerunner/scenarios/UnhandledExceptionEventDetailChangeScenario.kt
new file mode 100644
index 0000000000..62c880cf63
--- /dev/null
+++ b/features/fixtures/mazerunner/jvm-scenarios/src/main/java/com/bugsnag/android/mazerunner/scenarios/UnhandledExceptionEventDetailChangeScenario.kt
@@ -0,0 +1,75 @@
+package com.bugsnag.android.mazerunner.scenarios
+
+import android.content.Context
+import com.bugsnag.android.BreadcrumbType
+import com.bugsnag.android.Bugsnag
+import com.bugsnag.android.Configuration
+import com.bugsnag.android.OnErrorCallback
+import com.bugsnag.android.Severity
+
+/**
+ * Sends an unhandled exception to Bugsnag where the event details are changed in a callback
+ */
+internal class UnhandledExceptionEventDetailChangeScenario(
+    config: Configuration,
+    context: Context,
+    eventMetadata: String?
+) : Scenario(config, context, eventMetadata) {
+
+    init {
+
+        config.addOnError(
+            OnErrorCallback { event ->
+                event.apiKey = "0000111122223333aaaabbbbcccc9999"
+                event.severity = Severity.ERROR
+                event.groupingHash = "groupingHash1"
+                event.context = "new-context"
+                event.setUser("abc", "joe@test.com", "Joe")
+                event.addMetadata("custom_data", "test_data", "this is test")
+                event.addFeatureFlag("beta", "a")
+                event.isUnhandled = false
+                event.app.binaryArch = "x86"
+                event.app.id = "12345"
+                event.app.releaseStage = "custom"
+                event.app.version = "1.2.3"
+                event.app.buildUuid = "12345678"
+                event.app.type = "android_custom"
+                event.app.versionCode = 123
+                event.app.duration = 123456
+                event.app.durationInForeground = 123456
+                event.app.inForeground = false
+                event.app.isLaunching = false
+
+                event.device.id = "12345"
+                event.device.jailbroken = true
+                event.device.locale = "en-UK"
+                event.device.totalMemory = 123456
+                event.device.runtimeVersions = mutableMapOf("androidApiLevel" to "30")
+                event.device.freeDisk = 123456
+                event.device.freeMemory = 123456
+                event.device.orientation = "portrait"
+
+                event.breadcrumbs.removeLast()
+                event.breadcrumbs.first().type = BreadcrumbType.ERROR
+                event.breadcrumbs.first().message = "new breadcrumb message"
+                event.breadcrumbs[1].type = BreadcrumbType.ERROR
+                event.breadcrumbs[1].message = "Second breadcrumb message"
+                val map: Map<String, Any> =
+                    java.util.Collections.singletonMap<String, Any>("foo", "data")
+                event.breadcrumbs.first().setMetadata(map)
+
+                true
+            }
+        )
+    }
+
+    override fun startScenario() {
+        super.startScenario()
+        Bugsnag.leaveBreadcrumb("Hello1")
+        Bugsnag.leaveBreadcrumb("Hello2")
+        Bugsnag.leaveBreadcrumb("Hello3")
+
+        Bugsnag.notify(RuntimeException("UnhandledExceptionEventDetailChangeScenario"))
+        throw NullPointerException("something broke")
+    }
+}
diff --git a/features/full_tests/error_callback_alters_fields.feature b/features/full_tests/error_callback_alters_fields.feature
new file mode 100644
index 0000000000..3022062947
--- /dev/null
+++ b/features/full_tests/error_callback_alters_fields.feature
@@ -0,0 +1,53 @@
+Feature: When the api key is altered in an Event the JSON payload reflects this
+
+  Background:
+    Given I clear all persistent data
+
+  Scenario: Unhandled exception with altered event details
+    When I run "UnhandledExceptionEventDetailChangeScenario" and relaunch the crashed app
+    And I configure Bugsnag for "UnhandledExceptionApiKeyChangeScenario"
+    And I wait to receive an error
+    And the error payload field "events" is an array with 1 elements
+    And the exception "message" equals "UnhandledExceptionEventDetailChangeScenario"
+    And the error payload field "apiKey" equals "0000111122223333aaaabbbbcccc9999"
+    And the error "Bugsnag-Api-Key" header equals "0000111122223333aaaabbbbcccc9999"
+    And the event "severity" equals "error"
+    And the event "context" equals "new-context"
+    And the event "groupingHash" equals "groupingHash1"
+    And the event "user.id" equals "abc"
+    And the event "user.email" equals "joe@test.com"
+    And the event "user.name" equals "Joe"
+    And the event "metaData.custom_data.test_data" equals "this is test"
+    And event 0 contains the feature flag "beta" with variant "a"
+
+    # app fields
+    And the event "unhandled" is false
+    And the event "app.binaryArch" equals "x86"
+    And the event "app.id" equals "12345"
+    And the event "app.releaseStage" equals "custom"
+    And the event "app.version" equals "1.2.3"
+    And the event "app.buildUUID" equals "12345678"
+    And the event "app.type" equals "android_custom"
+    And the event "app.versionCode" equals 123
+    And the event "app.duration" equals 123456
+    And the event "app.durationInForeground" equals 123456
+    And the event "app.inForeground" is false
+    And the event "app.isLaunching" is false
+
+    # device fields
+    And the event "device.id" equals "12345"
+    And the event "device.jailbroken" is true
+    And the event "device.locale" equals "en-UK"
+    And the event "device.totalMemory" equals 123456
+    And the event "device.runtimeVersions.androidApiLevel" equals "30"
+    And the event "device.freeDisk" equals 123456
+    And the event "device.freeMemory" equals 123456
+    And the event "device.orientation" equals "portrait"
+
+    # breadcrumbs fields
+    And the event has 3 breadcrumbs
+    And the event "breadcrumbs.0.type" equals "error"
+    And the event "breadcrumbs.0.name" equals "new breadcrumb message"
+    And the event "breadcrumbs.1.type" equals "error"
+    And the event "breadcrumbs.1.name" equals "Second breadcrumb message"
+    And the event "breadcrumbs.0.metaData.foo" equals "data"