So, I have not yet called my home resort, but I have a couple of guesses as to what is going on.
Converted fixed weeks *do* pay one year in advance, spread out over the year. So, the monthly payments you make in 2011 *are* for the 2012 use-year. In contrast, UDI contracts pay during their use year. So, for UDI contracts, the payments you make during 2011 are for the 2011 use year.
Normally, converted fixed week resorts are billed the amount one year prior. So, during 2010, you paid the *2010* MF amount, rather than the (correct) 2011 amount, divided by 12, monthly. Then, near the end of the year, or possibly early in the next year, we would get a separate bill for the difference between 2011 and 2010 MFs. This is because, usually, most HOAs do not set the next year's MF amount until fairly late in the year prior.
So, I'm wondering---rather than billing us separately for the difference between 2010 and 2011---if the new monthly amount for 2011 includes both the usual increase from 2010 to 2011 MFs (for the estimated costs of 2012), *plus* the difference between 2011 and 2010 to account for the gap in the 2011 use year. That would make sense---that way they don't have to do separate collections for everything, and could fold it all into the "standard" monthly payment. And, it would actually be nicer for us; rather than paying the 2011-2010 deficit as a lump sum at the end of 2010, we can spread it out over 2011.
When I finally get my credit pool snafu straightened out (don't ask...) I will try to call my home resort and get the numbers for 2010 and 2011, to see if this holds water.