[GAMEPLAY] katarina w doesnt proc intended or bug?

kat's w doesn't have a cast time but her q does. When i Q and immediately press w during the cast time of q, it cancels the animation of q and the w procs right after the cast time of q. But when do a Q + W + R combo, pressing w during the cast time of Q, the W does not proc but instead goes straight away to the ulti. Just wondering is this intended or a bug maybe? It's kind of annoying that in order to do a full combo, I have to wait until the q cast time ends before I press w then R. (makes it significantly slower)