Playing SuperTux, I have so far found two bugs. I don’t know if they’re widely known, but anyway:
1. When you die (through touching an enemy / trap), the system first records your amount of lives left, and then checks if you have <0, and if you do it shows the game over-thingie and so forth. Bug: If you press escape while in the air after being killed (before the game over sign comes up) and choose Abort Level, you lose a life but the game over thingie never shows up and you never lose all your points. In other words, dying in this manner with your last life allows you to continue playing with -1 life. Next time, you get -2, etcetera.
2. I don’t quite know why this is, but still: If you choose to destroy an old save (pressing the delete button while in the Start Game mode), and then start a new game in one of the empty slots, you still have your old amount of lives and points from the last save. I don’t know why this is, but it doesn’t work if you quit the game in between deleting the save and beginning the new.