Why some scripts in the cron.hourly directory do not become executed

Because I have a very basic mp3 player that cannot play back anything but ISO-standard mp3s, I often need to re-encode podcasts which my podcast-catcher downloads (I use Amarok). I created bash scripts to re-encode all downloaded mp3s and to generate a new RSS feed based on the directory content where the re-encoded mp3s get stored. However, the scripts did not get executed every hour and the reason was their naming ("podacst_downsampling.sh"). There are quite strict rules how the names have to look like (which I don't remember), but if you use only a-z characters you should be always fine. After renaming to "podcastdownsampling" everything worked fine.