So I closed KMPlayer again. After having closed it, the hildon-thumbnailerd process went completely mental and started to use up 100% of the CPU - killing my battery in the space of a few minutes (only had a third or a quarter of the charge left to start with). That could be unrelated to KMPlayer though - not sure (come to think of it, I took a screenshot of KMPlayer while it was running so maybe the thumbnailer daemon is related to this instead).