I was going to leave that alone in the last post, but since you brought it up...
It didn't fail at Ueberlingen, DHL followed the TCAS RA but the Russian plane did not but followed ATC instruction instead. Had the Russians followed the TCAS RA, this collision would have been avoided.
Yes, the Russians followed ATC rather than their RA. However, TCAS re-calculates the appropriate manouevre during the RA sequence. In this case, it had given the DHL an instruction to descend. The crew subsequently followed their RA (as per SOP).
However, TCAS would have detected that the other aircraft was also descending, and this provides precisely the scenario above where the known software fault provided the "hole" (so to speak) for it to become confused when a mode reversal (i.e. a climb) should have been initiated during the initial descent RA.
Of course in hindsight a blanket "if everyone had followed their respective RAs then all would be well" sounds well and good but TCAS is supposed to re-calculate during the manouevre and a situation was encountered where that fault presented itself.