Weird sort behavior

Sorting is working on all but the last 100 rows of a 2100+ row spreadsheet. Why won't it sort the entire spreadsheet?

Relevant background: I recently took over this spreadsheet used as a membership database. It was spilt into two spreadsheets when an error prevented it from being expanded some time back (before my time with the spreadsheet). I'm trying to clean up the mess and recombine the spreadsheets into one.

I added columns to both spreadsheets so that the columns would line up properly and then copied all the rows from the smaller spreadsheet into the larger one. No problem.

But now, the sorting won't work on the entire spreadsheet. I've ensured that there aren't any completely blank rows or columns. And each column has a name.

If I select a smaller set of rows around the boundary area between the "old" and "new" data, it sorts those rows just fine. It's just when I select the entire spreadsheet that it doesn't sort the entire thing. [Actually, I purposefully don't select any of the spreadsheet to ensure that after picking my primary and secondary sorting fields, it should sort the entire database.]

I did not copy over the header row from the "new" spreadsheet.

Probably irrelevant background: There are formulas in a few of the larger spreadsheet columns that weren't copied into the smaller one so I've copied those into the cells from the smaller sheet as appropriate. Didn't make a difference, that I could tell.

I appreciate any help you can offer.

Thanks!

More information...

I hadn't tried to cut and paste the entire thing but when I did, that gave me some insight into what's going on - or not going on...

If I do a Ctrl-a (select all), it only selects 2027 rows and Z columns instead of 2129 rows and AE columns.

If I can solve this problem, the sort should solve itself - I think.