your order was probably partially filled that is why you got smaller amount of bitcoin back after cancelling it. go check your balance and also history and you will see these amounts check out.
ps. partially filled means for example you wanted to buy 40,000 satoshi of some altcoin so you placed an order of that size. then someone sold less than that amount to you. for example someone sold you 10,000 satoshi worth of that altcoin and then you canceled your order so you received 30,000 satoshi and you already have that altcoin too.
It is possible to happend like that RoommateAgrement.
Next time i keep my eye open and post it on cryptopia forum with screenshots.
That happend few days ago so i cant check every detail about it.
Anyway i just want to tell my experience.
I thought someone else also see something similar...