Tags disappearing

This has happened to me twice now. I have tagged all the apps I use with tags such as 'open source','audio','graphics' etc. Now I find that when I add more than one tag to an app, say I add the tags 'open source, audio', it saves them fine and the new apps show up in my tag clouds fine. But when I check back several days later I find that one or more of the tags and respective tag clouds has disappeared. It seems if you tag an application with more than one tag, it will drop one of the tags after a few days.

The first time this happened I figured it was just a bug that would be fixed so I left it for a few months and then re-tagged everything. Now I come back a few weeks after re-tagging everything and I find my tags are gone again. What is going on! Can you fix this please.