When adding or editing a tag with two or more albums selected, Picard hangs as soon as you 'save' the tag(s).

It makes no difference which albums are selected, or which tags are added or edited. 

I uninstalled, deleted the config files and cache, and installed a clean version with no plugins or major changes to the default options, and the bug was still there.

I first noticed this some time ago, so it probably affects some earlier versions, too. Perhaps it was introduced in version 2.5.