What MouseSavers is saying, and UT is saying (which contradicts the email they sent their customers), is that you get the current gate price at the time your ticket was sold. Actually, UT is saying and MouseSavers is hoping for, is when you bought the ticket, BUT Disney has no clue when YOU bought the ticket, only when your reseller bought the ticket.
IF you bought your ticket June 4, 2013, you will have stock no newer than the previous price increase, say May 2013 or September 2012 (same gate price). HOWEVER, depending on the reseller, your stock could date back to 2010 (or earlier) if you but from a reseller who moves product slowly--only a handful move quickly. Even if you bought from UT, who does move stock quickly, perhaps you got something that someone returned with their 'liberal' return policy. It could still be from 2010. And then, of course, there is the possibility that that person also got a restock, so maybe the ticket is gate priced at 2008. Long shot? Definitely. Possibility? Unfortunately, yes.
Disney only knows when THEY sold the tickets. They could change that going forward, but all of us that already have tickets, are SOL. I know I would have made some different decisions since I'm sitting on various tickets from trip changes 6 weeks ago when we were there.
I've had a few upgrading nightmares, but by knowing my facts, being sweet and polite, and very insistent/determined, I've always landed right. But I have no way to know my facts in advance now. And, Disney isn't always so flexible and nice. It might not be you, but the rotten day the CM has had to that point. And the way Disney has been cutting training the last 10-15 years, CMs simply don't know. The people who trained them don't know.
Safest bet from this point forward, even if you *think* you have everything nailed down, don't buy from a reseller. You might get more screwed in the long run. Plans do change unexpectedly. And, I for one, think that is what Disney wants.