Repro:

1. Paste the following code into a C# file:

class C
{
    public string Foo = "foo"
}

2. Put a breakpoint here at the beginning of GetFormattingChangesAsync.
3. Insert semicolon after "foo".
4. After the breakpoint is hit, step over. Hit "Cancel" when this dialog pops up:
   
5. Continue with code execution.
6. Observe double semicolons being inserted:
   

cc @uniqueiniquity