Lite-C for some reason messes up with bigger shapes.
I don't know what is going wrong. The code for triangulation is clearly written not nice. In fact it is extremely ugly.
Maybe there is still a flaw hidden where I forgot to patch the code for Lite-C or some internal stack has problems (doubtful).
Anyway I could not solve this and now I compiled all the mess into a DLL and use this one from Lite-C. This works fine.
...and it shows off a big problem of Lite-C. Porting things should not be such a hassle.