While downloads should begin having matching version numbers immediately (the download script was modified to handle this), the caching issues should be fixed in the next release.
This was actually not working as designed: it was not caching at all, and if it would ever, it would never be cleared by an upgrade. I spent a long time today trying to resolve an issue with session locking when trying to debug this on the same server as the version check script. I'm not sure how it ever worked for me in the past, or if the session lock just started occurring after clearing the Xcache for a certain PHP file, but either way, it's not possible to test this locally anymore.