The trickery trait Flanking Strikes does, in fact, not gain any ACTUAL cooldown reduction on the applied haste, as indicated by the tooltip, from the trickery trait Trickster. This breaks one of the main synergies for the specialization tree, and overall hurts the class. Additionally, flanking strikes no longer has any synergy with Improvisation from the deadly arts tree, in a similar manner.
Summing up, flanking strikes hasn’t been a Trick type skill since the bug fix when HoT launched, which means none of the traits relating to tricks affect it, regardless of tooltip updates. Takes literally 48seconds to test this out, PLEASE FIX. Thanks