You may be fighting against what used to be the slower classes. They used to switch their guards at a slower speed. That has been changed and all classes switch at the same speed now. That's the only difference I can think of, PK hasn't changed, but it may look like she has when you see that you can't change faster than some of the other heroes anymore.
I thought it was just me might be something they need to look into, I swear it's like she locks and stands still when I'm switching attack directions or blocking different directions quickly. Could be like back in the halo days when you could glitch your guy by overloading him with inputs making his animation get frozen
We equalized guard switch speeds back in 1.08.01 - patch notes here - so that may be what you're experiencing.