Can Outlook Sync delete data from NAV?

I am trying to delete to-do entries from Navision, when they get deleted in Outlook calendar, however... it seems, synchronization at first send signal to delete data to navision, but then recreates same entry in outlook again.

Have anyone of you tried to do similar thing? (I have setup bidirectional synchronization between nav and outlook - when only some fields are changed in outlook or navision, these changes are reflected both ways, but I still cannot delete data from outlook).