There are two sets of "Blocks" and "Depends On" fields in the buglist.cgi form. Don't know when these popped up. Only one set actually works, even though it may look like both sets work. One set needs to be removed to avoid confusion and maintain proper use.
Clarification: Must click on "change several bugs at once" to get to the bulk changing form.
Thanks Andrius. This will be fixed in the next update.