Ah. There is a minor bug of sorts, though not necessarily what you'd think.
Early in our OT development, we thought it was okay to have a font that was indicated as being bold-styled, even when there was no base font that it was the bold version of. Later, we changed our minds on that score.
Myriad Pro was one of the very first OT families we released, so it was built the first way. The "Black" weight is indicated as having a bold style, even though there is no other base font.
This is a relatively benign issue in this case. However, I will file a specific bug so that the next time we have occasion to revise the font, we change this.
Regards,
T
Thomas Phinney
Program Mgr., Western Language Fonts
Adobe Systems