It does seem rather unlikely that having descended to a level 1000above the dash 8, that TCAS would command a further descent..........it doesn't work that way.
Seems that this is what actually happenned. We'll wait for the final investigation to take place but the results I fear will not be in favour of TCAS. This has happenned before on a much less severe scale, and is triggered by high rate of descent/climb, TCAS assesses the closure rate and decides to act accordingly. Its why ATC, when able, will give traffic info to IFR in Classes A/B. Our conflict alert will be activated, so we ensure both aircraft are aware of each other and re-inforce the cleared levels. I say 'when able' as its not a requirement, and there are times when far more important things need to be done.