adding the plugin changes the runtime behavior (withOverrideScalaVersion(false))

[eed3si9n]

This was originally reported as sbt/sbt#4525 by @zella

steps

1. git clone https://github.com/zella/sbt-issue
2. sbt run

problem

[error] Caused by: java.lang.NoClassDefFoundError: scala/math/Ordering$$anon$9
[error]         at scala.tools.nsc.transform.LambdaLift$LambdaLifter.<init>(LambdaLift.scala:67)
[error]         at scala.tools.nsc.transform.LambdaLift.newTransformer(LambdaLift.scala:49)
[error]         at scala.tools.nsc.transform.Transform$Phase.apply(Transform.scala:30)
[error]         at scala.tools.nsc.Global$GlobalPhase.$anonfun$applyPhase$1(Global.scala:426)
[error]         at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:419)
[error]         at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1(Global.scala:390)
[error]         at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1$adapted(Global.scala:390)
[error]         at scala.collection.Iterator.foreach(Iterator.scala:941)
[error]         at scala.collection.Iterator.foreach$(Iterator.scala:941)
[error]         at scala.collection.AbstractIterator.foreach(Iterator.scala:1429)
[error]         at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:390)
[error]         at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1446)
[error]         at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1430)
[error]         at scala.tools.nsc.Global$Run.compileSources(Global.scala:1423)
[error]         at scala.tools.nsc.Global$Run.compile(Global.scala:1539)
[error]         at org.fusesource.scalate.support.ScalaCompiler.compile(ScalaCompiler.scala:89)

No failures without addSbtPlugin("com.lucidchart" % "sbt-scalafmt" % "1.16")

expectation

No failures.

notes

By default sbt uses Ivy mediator to enforce scala-library and scala-compiler to line up (sbt/sbt#2634), but neo-sbt-scalafmt turns that off.
https://github.com/lucidsoftware/neo-sbt-scalafmt/blob/1.16/sbt-scalafmt/src/main/scala-2.12/com/lucidchart/sbt/scalafmt/Platform.scala#L42
The fact that introducing this plugin changes the semantics of the build is very surprising to me.