I know you said the field was "formatted as a date". Is it of type "date"?
If it is of type date, I'd want to rule out the possibility of hidden damage in the original file. Try recovering the FM 8 file and then import from the recovered file into your FMP 10 clone.
Sorry, I was imprecise (I always complain to my clients when they do that to me).. Yes, it is type date. I'll have to wait until Monday to get the "original" FM8 file (at my client's office) and then I'll give it a try. I'll let you know the outcome. Thanks.