I remember a cooldown like that before in previous releases and since I don't see it every time, I didn't think it was a big thing.
However, Cordovan, if it is supposed to happen every time: it is not. Are there any rules around it, like hot swapping main hand only, offhand only, swapping main and off only? I just want to make sure that I am understanding the change so I don't file a useless bug report.