Pan,
Packet Paging are carried by PCH (on BCCH).
A Packet Paging might occur (rarely, I agree), if the subscriber have sent an UL data, and the internet is taking time to answer.
The UL TBF is released, the DL TBF is not yet allocated, the MS is entering in Packet Idle Mode. Only a Paging can wake him up, so that it can prepare for the DL incoming data 🙂
But I agree, it happens rarely.