Oh, btw I almost forgot:
Some weeks ago I accidentally started Marble by clicking the wrong icon. I noticed it before the map was even loaded and closed the application window immediately which apparently worked.
Some hours later I noticed a big battery drain and top showed that Marble was still running and constantly consumed about 50% CPU time. So I killed it and everything was back to normal.

Not sure if this even qualifies as a bug but it's definitely an unexpected behavior.