With a monk, I was using Shenlong's fist of legend (first hand) and Echoing fury (second hand), then switched Echoing fury with my shield by right-clicking it. At this point my attack speed bugged, it was at 1.15 (my default attack speed without weapons) while Shenlong's was equipped (which has 1.40). Switching from no weapon equipped to Shenlong's did not change my attack speed, it stayed at 1.15 in both cases. I changed Shenlong for Echoing fury, and my attack speed was now at 1.44 (while my Echoing fury has 1.45 base attacks per sec). The bug ceased when I re-equipped both weapons I had before the bug. I could not reproduce this error afterwards.

Skill used: fists of thunder: thunderclap
act 2, black canyon mines fighting a fallen elite pack