Yes, you're at the right spot.

Ok so I modified my small program to give something like the desired behaviour:
Drop Box link to X11Test Code Blocks project
Can you confirm?

actually, after much tinkering I got the original code to work so it must be something else

Ah, that's what the chat post was hinting at. Hm. So the old code works... sometimes?

It works in my demo program X11Test but not when used in the Kore Mouse.cpp file. The Linux specific file, that is.

Oh, that's mysterious.

that is bazaar There must be some subtle difference that I will have to find. It's one of those unreported errors because "The show must go on!" type deals.

do you mind if I use GLX calls?
that is between:

#ifdef KORE_OPENGL
...
#endif

Yes (just for the record, already talked about it in irc).

so yeah, done. The answer to the puzzle was glXGetCurrentDisplay().