I just discovered this problem last night. I use Cubase. But I've found the bleed issue happens with all programs on my Macbook Pro. I created a test .WAV file with sound hard-panned left, no signal at all on right. Through iTunes, Cubase, Quicktime Player, etc., I hear a dull bleed through the right channel. The overall balance is left, but it's NOT hard-panned. Even through a USB audio interface! If the Macbook itself is playing the sound, through any output, there's bleed. However, I synced up that file to my iPhone through iTunes and, with the same headphones plugged into the phone, I get no bleed, like it's supposed to be.
It sounds like this is an internal problem on Macbook that cannot be fixed. Funny, though, is that under the System Preferences, you can hard-pan the output of the whole machine (which there's really no need for, unless you're permanently hooked up to some sound system that needs to be corrected), and THAT seems to isolate channels completely. So the problem is somewhere internal between there.
The whole reason I bought this Macbook was for music production, since all along Macs have been touted as better for this kind of thing. This is unacceptable and frustrating. I don't like the solution to this being "use a PC instead."
