I've noticed that....
Stuff like Ferocity and Raging Strike create a buff that goes away after a successful attack... but most times "Cadence" doesn't go away, making you think one of the circumstances which would cause it to activate haven't been met...
I'm not sure if it is a bug, but I've definitely noticed it too.. and I only used it manually...
Sometimes it would work...
The problem is stacking WS in a battle reg automatically raises their power, so you can't really tell if Cadence has worked... especially when the buff stays up until the timer runs out