I had the exact same thing when I looked at my fees online yesterday. (I bought 160 points on July 24, but didn't close until later in August. My UY is April.) I called yesterday, and MS Accounting told me that it is 4 months of dues from 2007 (Sep, Oct, Nov, Dec) that I have to pay:
160 x $4.62 = 739.20/12 months = $61.60/month
61.60 x 4 months = 246.40 ($247 according to Disney's calculations - I've found that they do love to round up!)
Now, since September first has already passed, that $247 needs to be paid in 3 months, thus 82.33/month payable on 10/1, 11/1, and 12/1.
When I initially signed up, I told them that I would pay my maintenance fee in a lump sum rather than monthly. When I talked with them yesterday, I changed it to debiting my account monthly, just like they do my loan. They may have you in the system as a lump sum payer even though you told them otherwise.
Hope this helps!