only sent content resolution if it's needed
The PCU is always sending the TLLI in the RLC/MAC even when the content resolution is over.
This would save some 32 bits per RLC/MAC
I don't remember seeing this behavior you mention here in ttcn3 PCU_Tests. I'd need to check again but I'd say that's in general working correctly (no TLLI sent after contention resolution).
It may be however that I was focused on checking what the MS side was sending instead of the PCU.