On windows if you jerk her off to the left, during the orgasm her penis swings to the right and you can't control it, and it sometimes misses the bucket. Seems to be more consistent if you jerk her off to the right, but that's really annoying
Edit: Okay, upgrading the bucket makes it bigger, so that fixes the issue. For new players, the demo only lasts a few minutes, you will need to spend $5 to continue to play the game. And milk volume is the most important upgrade. Also buying new machines has new girls, upgrades, and items. That means items in one area (e.g. stamina bottle in the hands area) can only be used on hands-area girls, not new machines.