Examine the field options for those two fields to see why this is happening. Best guess is that either these fields are defined in a different table or that an auto-enter setting is auto-entering data during the import process. If it's an auto-enter setting, you can either disable auto-enter operations during the import (there's a check box for controlling this option that pops up just before the import starts), or you can temporarily disable the auto-enter options on these fields just before importing (Which can allow you to leave other auto-enter operations that you want to take place free to do their thing.)
Those specific fields were set as "global" fields and turning global off fixed the problem. Thanks!