Program: 161428
Project: 161428
Buggy source:
@Override public Result preprocessEnter(@NotNull final PsiFile file,@NotNull final Editor editor,@NotNull final Ref<Integer> caretOffset,@NotNull final Ref<Integer> caretAdvance,@NotNull final DataContext dataContext,final EditorActionHandler originalHandler){
  final Result result=skipWithResultQ(file,editor,dataContext);
  if (result != null) {
    return result;
  }
  Document document=editor.getDocument();
  final Project project=editor.getProject();
  PsiElement atCaret=file.findElementAt(caretOffset.get());
  if (atCaret == null) {
    return Result.Continue;
  }
  if (!(atCaret.getParent() instanceof FunctionCall && atCaret.getNode().getElementType() == MathematicaElementTypes.RIGHT_BRACKET)) {
    return Result.Continue;
  }
  final int offset=caretOffset.get();
  final int lineNumber=document.getLineNumber(offset);
  final int lineStartOffset=document.getLineStartOffset(lineNumber);
  final int prevLineStartOffset=lineNumber > 0 ? document.getLineStartOffset(lineNumber - 1) : lineStartOffset;
  final EditorHighlighter highlighter=((EditorEx)editor).getHighlighter();
  final HighlighterIterator iterator=highlighter.createIterator(caretOffset.get() - 1);
  final IElementType type=getNonWhitespaceElementType(iterator,lineStartOffset,prevLineStartOffset);
  if (!separators.contains(type)) {
    return Result.Continue;
  }
  originalHandler.execute(editor,editor.getCaretModel().getCurrentCaret(),dataContext);
  if (project != null) {
    CodeStyleManager.getInstance(project).adjustLineIndent(editor.getDocument(),caretOffset.get() + 1);
  }
  return Result.DefaultForceIndent;
}

Fixed version (ground truth):
@Override public Result preprocessEnter(@NotNull final PsiFile file,@NotNull final Editor editor,@NotNull final Ref<Integer> caretOffset,@NotNull final Ref<Integer> caretAdvance,@NotNull final DataContext dataContext,final EditorActionHandler originalHandler){
  final Result result=skipWithResultQ(file,editor,dataContext);
  if (result != null) {
    return result;
  }
  Document document=editor.getDocument();
  final Project project=editor.getProject();
  PsiElement atCaret=file.findElementAt(caretOffset.get());
  if (atCaret == null) {
    return Result.Continue;
  }
  if (!(atCaret.getParent() instanceof FunctionCall && atCaret.getNode().getElementType() == MathematicaElementTypes.RIGHT_BRACKET)) {
    return Result.Continue;
  }
  final int offset=caretOffset.get();
  final int lineNumber=document.getLineNumber(offset);
  final int lineStartOffset=document.getLineStartOffset(lineNumber);
  final int prevLineStartOffset=lineNumber > 0 ? document.getLineStartOffset(lineNumber - 1) : lineStartOffset;
  final EditorHighlighter highlighter=((EditorEx)editor).getHighlighter();
  final HighlighterIterator iterator=highlighter.createIterator(caretOffset.get() - 1);
  final IElementType type=getNonWhitespaceElementType(iterator,lineStartOffset,prevLineStartOffset);
  if (!separators.contains(type)) {
    return Result.Continue;
  }
  originalHandler.execute(editor,editor.getCaretModel().getCurrentCaret(),dataContext);
  if (project != null) {
    CodeStyleManager.getInstance(project).adjustLineIndent(editor.getDocument(),caretOffset.get() + 1);
  }
  PsiDocumentManager.getInstance(file.getProject()).commitDocument(document);
  return Result.DefaultForceIndent;
}