This is a very very old bug, it was well known during betas before Proph release, I reported it myself too back then, but nothing has been done. It affects various animated textures, not only Storm Bows but also all Tormented weapons, many other weapons, and other stuff like burning fires.
Restarting game is probably the only 100% certain solution, it sometimes fixes itself after even longer play but you can't count on that.