Possibly related to CONF-30084:

I set up a new Confluence 5.2 system and installed a plugin which contains a PluginUpgradeTask defined in the manner suggested by Atlassian.

Next, I went to Admin->Backup & Restore and told it to restore a previously-saved XML backup of a Confluence 5.1 system.

The restore seems to complete successfully, but the PluginUpgradeTask in my plugin is never run. The plugin is fully operational, except my persisted username data is never migrated to user keys, which poses a big problem.

If I then go to the UPM and upload the plugin again, the PluginUpgradeTask does run successfully. (If I shut down and restart the system, I get hit by CONF-30084 problem and the system never comes back up.)

Analogous to CONF-30084, the PluginUpgradeTask does get run if the upgrade is performed in other ways (such as by doing a fresh Conf 5.2 install and feeding it the 5.1.x XML during the initial setup, then installing the plugin after the restore completes). It's just the admin-section-initiated restore that seems to be having problems.