WordPress + IIS + Wincache = plugin update trouble

A while ago, we started having trouble updating our wordpress plugins (and wordpress itself). Updating a plugin would fail with a "Could not remove the old plugin". The plugin directory is there, but empty, and strangely cannot be deleted. We’ve found that restarting the app pool seems to resolve everything, even allowing the auto-update to work correctly.

We finally found the root cause. It’s a known issue with wordpress and the version (1.1.630.0) of wincache we’re using. Updating to the latest development build (1.2.1209) seems to have resolved the issue.