So tried it in different browsers:
Firefox: flush (exactly)
Chrome: flush (exactly)
Safari 5: not flush (only 2-3 pixel)
IE 8: not flush (olnly 2-3 pixel)
IE 9: not flush (only 2-3 pixel)
Opera 11.10: not flush (5-7 pixel, like in the image above)
I think there must be a problem with (percentage) the interpretation of the with relating to the number of modules (currently 3) in this position.
Hope you can find the problem.
Regards!