You have hit a bug. Throughout the life of version 7, power users reported it formally and informally to Extensis and asked for it to change. Given the few changes that Extensis made with version 8, you've got to wonder what their programmers have been doing for 18 months....
If you're interested, the fault is essentially that their resizing calculation assumes the originals are at 72dpi. Now don't ask me the relvance of resolution when your program is just resizing images to fit into a given number of pixels. The proof is at http://www.portfoliofaq.com/pfaq/downloads/prevSizeCheck.htm
As for a fix, I change my film scans' dpi to 300 in Photoshop. Maybe your problem is that you have left Resample Image ticked?