Bug: Cancelling attacking with autoattack creatures

Hi, I wasn't sure if there was a thread to report bugs and this doesn't technically qualify as "feedback" so I've made this thread.
There seems to be a bug in XMage that allows you to cancel attacking with creatures that are required to attack every turn. When playing against someone yesterday using a common Rabble Red build, he went into combat with two Goblin Rabblemasters in play. While he was declaring attackers, he found that he could actually cancel the Rabblemasters and their tokens from attacking. He wasn't doing it on purpose, I guess he was just experimenting, but it seems to be an obvious bug of some kind.
Anyway, that's all. I hope I posted this in the right place!
There seems to be a bug in XMage that allows you to cancel attacking with creatures that are required to attack every turn. When playing against someone yesterday using a common Rabble Red build, he went into combat with two Goblin Rabblemasters in play. While he was declaring attackers, he found that he could actually cancel the Rabblemasters and their tokens from attacking. He wasn't doing it on purpose, I guess he was just experimenting, but it seems to be an obvious bug of some kind.
Anyway, that's all. I hope I posted this in the right place!