Regarding the previous query, yes I got it sorted out. The problem at the time was that if I send 1 or 2 PDAs after sending PUAN then both are ignored, but if I send 3 PDAs after PUAN then I get PCAs for all three.
I still don’t know why that happens, but once I’ve sent PUAN (with FBI set) then the MS considers the TBF ended, and it stops monitoring the PDCH. So strictly speaking I shouldn’t ever have received a PCA for the PDAs sent after PUAN. It may be a quirk of the handset firmware (Nokia) that the MS responds to the 3x PDAs even though it shouldn’t.
Regarding the current thing, I’m only using non-extended mode TBFs, so things should be fairly straightforward. I am running with a short value of T3192 at the moment (80ms) so if I have a sequence of DL TBF 1 -> UL TBF -> DL TBF 2 then there should be no risk that DL TBF 1 is still active by the time I get to DL TBF 2. Still testing to see how it works out…