It used to just happen underwater after the last patch but more and more I am getting it on land. When I drop a banner then pick it up all my weapon skills stop working. I have confirmed this with my other guild members as a bug. Dying in pvp fixes this but in wvw I have to relog to get my skills working again. The queue times are astronomical right now so this bug is a game breaker.
Also in wvw after the bug I somehow get infinite endurance. So I can dodge roll as many times as I want.