The reason you'd want to select text is to select text... same inside a text field disabled or not as outside a form field. Unless you think they should just disable all text outside an active form field?
I'm not saying I agree with the implementation -- I think the text should indeed be selectable. But it's not what I would call a bug. I looked at the Bugzilla ticket type system and it should be an "enhancement" or "task", not a "defect".