"Configure language specific settings" not working with new setting ui.

[heroboy]

Version: 1.27.2 (user setup)
Commit: f46c4c4
Date: 2018-09-12T16:17:45.060Z
Electron: 2.0.7
Chrome: 61.0.3163.100
Node.js: 8.9.3
V8: 6.1.534.41
Architecture: x64

Steps to Reproduce:

1. Ctrl + shift + p and choose "Preferences: Configure language specific settings..." see
2. In the open setting ui, set "Files:encoding" to "gbk"

expected:
in the setting json file it will be

"[bat]": {
        "files.encoding": "gbk",
 }

actual:

{
    "files.encoding": "gbk",
}

Does this issue occur when all extensions are disabled?: No

Another question : why the batch file key in setting file is "[bat]" not "[batch]", not like it should be "[typescript]","[markdown]" not "[ts]","[md]"