Foul when potting opponent's ball (during 8-ball)

[lulstrats]

Apparently even when you make a LEGAL shot (cue ball hits your ball first), it is still considered a foul if an opponent's ball is pocketed inadvertently during the same turn. I understand if the 8-ball gets pocketed before it's time to do so, but why the foul for pocketing opponent's balls?

I've played 8-ball at local pool halls for years and years, and have never heard of such a rule. I've watched official APA Pool League games and players have pocketed their own ball + opponent's ball on the same turn as a STRATEGY SHOT (opponent purposely blocking pocket) without receiving a foul.

Anyone at Cherry Pop Games want to enlighten me?

[Qugar]

Maybe you mixed up blackball with eight-ball? As far as I know it is a legal move in blackball but in eight-ball like in this game it is a foul. But I'm not 100% sure.

If you pocketed the 8-ball and an oppenent's ball in the same turn, then it is a foul anyway. "APA Game Rules" paragraph eleven.

[LonelyBacteria]

always knew it being that way