Autoblog intermittently drops specified tags

I've used Autoblog to setup multi-site blog that aggregates feeds from a number of sources. I'm using unique tags for each feed and I've set these in the Feed admin panel -- seems the easiest way to identify content from each source.

My problem is that Autoblog intermittently omits the specified tags. There doesn't seem to be any pattern. It works fine for a while, then omits tags for a few updates, then it works again.

Any ideas on how to resolve this (or at least how to diagnose the problem) would be greatly appreciated.