Am I missing something here? Casting seems to change based on click to move vs WADS

Some skills seem able to be cast while moving while others moving interrupts the cast yet they all have cast times? Like if i'm moving I can cast spark while moving but flame wall? Nope, if I clicked to move after hitting the flame wall hotkey the flame walls animation and cast was interrupted.

Casting seems to change how it works with WADS movement though. I can now move while casting flame wall, the movement doesn't interrupt it...

It seems stupid and wrong for this to be the case :S

Having to stand still during the waves of adds and the leaps on Geonor in act 1 to be able to flame wall while being pounded by the enemies or just not use the skill at all made the fight so hard lol. If I didn't use the skill the adds built up but if I stopped to cast it they killed me.