TBB 5.0 Bug 16771 which seems to be causing a lot of crashes was apparently introduced with commit 77dcb2dfde4bdc1a2f6c399a1173f65908dccd5c on 2015-07-02 (new request isolation feature). The first release including that commit was apparently TBB 5.0a4 announced 2015-08-03.

So there was only 1 week before the stable TBB 5 release and the commit got very little testing.

IMHO, it would make sense to make more alpha releases and/or increase the time before the stable release.