Hi!
This problem is caused by the bug that the last row is omitted by the import process. The bug is already fixed in the 5.1.1 that can be downloaded for beta test here:
http://www.x-cart.com/downloadxc5beta
In order to work around this issue in X-Cart 5.0.12 just add an empty row at the end of your CSV file and it should work out.
Tony.