Forum .LRN Q&A: notification_request__new never returns

Ok, I'm completely stumped, and am hoping someone out there has some bright ideas.

This site was installed with the beta copy of 4.6.  Everything was fine until 4.6 came out, and I upgraded.  I used CVS to upgrade the files, and implemented the one SQL change (host_node_map, as I recall).  I figured this was fairly safe since there wasn't time for many changes between the beta and final releases.

Since I did that, however, we can't add users to classes or communities anymore.  I've traced it down to notifications_request__new;  my Notice at the very end of that shows up in the log, but the one in package_instantiate_object that comes immediately after the call does not.  So for some reason, notifications_request__new is not returning to the caller.  The thread hangs and eventually the entire site stops responding, although scheduled procs still run.  There are no errors in the error log.

I cannot seem to figure out why this is happening.  Where does a return go, if it doesn't go back to the caller???  I suspected memory corruption but the problem survived a reboot, and it's too consistent to be a bad bit.

I should also mention that I'm not 100% sure it's due to the upgrade - but the timing seems suspicious.

Anyone else seeing this, or ever seen anything like it?