Unusual custom field problems

I’ve recently upgraded to 2.1.3, and noticed that the plugins which relied on custom field functionality (Cricket Moods, cocomment enhancer, etc) seem to work erratically. I haven’t yet debugged them at length due to time constraints, but it appears that they can no longer delete_post_meta, which results in duplicating custom fields at least some of the time. I end up having to manually delete the relevant database records.

Did something change in that part of the API?

I have turned on caching and eAccelerator — could it be that it’s a caching issue somehow?