I think I fixed that problem. See this [PR](https://github.com/nim-lang/Nim/pull/4530/files) may be fixed in Nim devel soon, if Araq does not tell me I did everything wrong... again :P
EDIT: As I already knew .. but this [PR](https://github.com/nim-lang/Nim/pull/4531) probably makes it and fixes this and related problems.
