a) Chesty, I read your post properly and realized you described exactly an opposite result. In that case, could it be you were equipped with 6.x version in RVSM levels during a 1000 ft level off encounter?
b) found the picture:
time threshold value is further reduced from 30 s to 25 s in order to provide a few more seconds to detect a possible leveloff manoeuvre of the intruder and thus to avoid the triggering of the RA. This should decrease the number of RAs for level aircraft triggered by aircraft levelling off 1000 ft above or below.