I have a strange problem. I have problems with deleting appointments on my phone. The appointments are deleted on the phone but not in Groupwise. Deleting the appointments in groupwise deletes them also on the phone. Creating appointments works both ways. What could be the problem?

Deleting items :

Phone -> Groupwise not working
Groupwise -> Phone works

Creating items :

Phone -> Groupwise works
Groupwise -> Phone works.