attacking interrupts casting

It seems that quickly attacking after casting a spell with cast time interrupts the spell. I only noticed bc i tried to cast a curse with expanse and wondered why it wouldnt go off sometimes. The spell is on cooldown from expanse but no curse happened. The cast time is also just 0,7 sec so you have to attack probably within 0,3 sec or so but its noticeable in a hectic fight with lots of spamming your attack button.