Getting interrupted not actually interrupting you

When casting any spell with a caste time if you get interrupted by a mob you can cast another spell right away and the previous spell still goes though after the time it would have taken when you first casted the original spell

 

Did some more testing you need to have prevent movement while casting checkmarked for this bug to work... I tested with it unchecked and it does not reproduce. But i also got a bug that interrupted me the INSTANT I casted any spells that had a caste time. (this was with prevent movement while casting UNCHECKED)