I've never seen this problem. Are you importing between 2 different versions of TYPO3? I recommend running an advanced search at http://support.typo3.org for hints. This is where I go 90% of the time when I get stuck 
Gregory Remington
Mediatech Consulting, Inc.
Phone : +1 (760) 525-1770 . Fax: +1 (760) 542-1990 . Skype: gremington
Gregory Remington
Mediatech Consulting, Inc.
Phone : +1 (760) 525-1770 . Fax: +1 (760) 542-1990 . Skype: gremington