I've managed to launch bottles even when the bottles are tightened down so hard I need TWO hands (while stopped!) to pull them out. The force from a rear bump seems to hit the bottles exactly right, unfortunately.

I've since abandoned the X-wing setup and gone to aerobar and downtube bottles. When training, I'll actually put the bottles in my jersey pockets. That rear rack is a real bottle launcher. Rubber bands prevent this, but also make it hard to remove them.