After some work I realized that I need to keep everything as it is, only change from cubic to quadratic or the other way round. I went for cubic -> quadratic. The conversion doesn't has to be perfect. All tools add extra points. I found out that the simplest conversion from cubic to quadratic is to offset offcurve points to 75% of their lengths. I am using brutal way of changing it with xml parser. I see that when I cmd + c a cubic contour to quadratic or the other way around font I get the desired result, which I am not able to access via code though.

@frederik Excellent, thanks!

I'm aware of that option and this will be implemented, but still there is something wrong with the provided data to the binary ttf compiler...

Thanks Jens its seems to be a fontTools issue :) http://sourceforge.net/p/fonttools/code/ci/master/tree/Lib/fontTools/ttLib/tables/_g_l_y_f.py#l549 it seems to recalculate the bounds from all points instead of analysing the bounds of the contour (this will be fixed in the next version...

Thanks, that did it! :)

Did some tests and this issue is already solved. It will be in the next update.

the ttf "path": RF UFO > internal ttf compiler on top of ufo2fdk > glyph data .ttf > fdk for some tables > .ttf

RoboFont will check the splines and convert them to two off curves splines in the next version. (in version 1.1 it doesn't check WOFF files, but it should :) Although WOFF files with PS outlines should work fine. Bonus answer: no ;)