Scroll success rate purposely or bug?

Recently, I collected and bought alot of Maple Coins, and exchange for Chaos Scrolls. I also found alot of Amazing Chaos Scroll and normal Chaos scroll from MesoRanger event.

But, I dare say that 7-8/10 are failure, I also looking through forum and found out other people also whining about it. Do you think it is purposely or bug?

IMO, I think it is purposely from A$ia'$oft-balls, they purposely lower the rate trying to trick people with original % written on the description. So player would get buy those Pam Songs.

I think the next cash shop update or after MesoRanger ends, would be the return of Pam Song...

So, what do you think?