[TYPO3-mvc] FrontendUser has no Groups

[Thomas Mammitzsch]

Hi list,

i have a Domainmodel Tx_Ptferegister_Domain_Model_frontendUser which 
extends Tx_Extbase_Domain_Model_FrontendUser. If i try to get all groups 
, which the user is in, i get an empty array. The user is in groups 
5,9,10 (set via Backend). Accessing other properties works fine. I'm 
using extbase 1.3.0.
Anyone got an idea for this one?

Regards, Thomas