I got the same issue when importing excel and tab delimited text files. If you press the prev. button to return to the spreadsheet form after starting to map the fields to be imported, and then return to the mapping form, the fields you had previously mapped are still there but the dropdown box is no longer active and text is able to be entered. You must cancel import at this point and start over.
Another problem I have encountered on the mapping form is when importing fields that contain text date values. Import will not allow more than 2 text dates to be imported in the same record. The first two dates are imported, the third date is ignored. Really! I’ve tried it many times!
I can send you a solution if you would like.
A third problem on the mapping form occurs if two dates have the same value on the left side of the mapping form. The right side will try to force the field mapping from the first field to the second field (see attachment)
Using rc2 on Win2k