Sorry about the initial bugginess; definitely not the best way to introduce changes. Should all be working now, but please let me know if you run into something odd.

> What if there have been a rash of Qs that are duplicates, with people possibly being driven to post the same thing repeatedly precisely because there has been no accepted solution yet?

In practice, this is pretty rare. To the extent that I would consider it one of those "exceptional" situations moderators are supposed to be useful for. 

That said, here are all the questions from the past 90 days where at least one vote would've been impacted by the "must be answered" restriction: 

http://superuser.com/q/486694  
http://superuser.com/q/492644  
http://superuser.com/q/499072  
http://superuser.com/q/505683  
http://superuser.com/q/507612  
http://superuser.com/q/512510  
http://superuser.com/q/512524  
http://superuser.com/q/514916  
http://superuser.com/q/516971  
http://superuser.com/q/516994  
http://superuser.com/q/520198  
http://superuser.com/q/521133  
http://superuser.com/q/522261  
http://superuser.com/q/523322  
http://superuser.com/q/528602  
http://superuser.com/q/533005  
http://superuser.com/q/533152  
http://superuser.com/q/533566  
http://superuser.com/q/537307  
http://superuser.com/q/540514  
http://superuser.com/q/540540  
 
<sup>(Note that some of these are closed as duplicates of multiple questions, some collected close votes that weren't "Exact Duplicate", and some ended up being closed by moderators anyway)</sup>

Look 'em over, see what you think.