For the purposes of BFC, a "mirror matrix" reverses the windings, and so must be detected by the rendering engine and dealt with automatically. BFC doesn't care about the actual final geometry, so the fact that it also creates a mirror image doesn't apply to the BFC spec.
The following from the spec should answer your other question (emphasis added):
The following from the spec should answer your other question (emphasis added):
Quote:Marking a file as BFC-compliant only directly affects that file. In order for subfiles to be treated as compliant, they must also be marked as compliant. Additionally, with the exception of parts, a file is only treated as being BFC-compliant if it and all of its superfiles are compliant. The reason for this is that, while processing, there is no way to know the intended inversion state of a subfile when the file's superfile isn't BFC-compliant. The reason that part files can be excepted from this rule is that they are complex closed solids, so there is never a valid reason to invert them. Assuming part files are never inverted allows the rendering engine to apply BFC-processing on certified parts, even if the calling file(s) (for example, the main model file or sub-models of the main model) aren't certified.