Hi Phil,
This is a by-product of the new FDX interface. They no longer use real account numbers, but pseudo account numbers, as described in the instructions. One feature of FDX is improved safety over your login credentials and account numbers. They are no longer provided to Fund Manager in any way. Instead of the real account number, Schwab makes up a pseudo account number, specifically for Fund Manager and this account and the FDX interface.
Where exactly are you using account numbers for display purposes in reports? In the header? Some column? Which report type are you looking at?