Top-level non-BFC models can contain mirroring, and BFC-compliant renderers will still render them properly, with BFC force-enabled for BFC-certified parts. Any software that supports BFC really needs to support enabling reset of BFC when rendering a BFC-certified part, because most user models don't specify BFC. Not doing this would result in BFC having no effect in most models. This also requires tracking the "matrix flip" state of all models, not just BFC-certified ones.
LDView keeps two sets of geometry: BFC-certified geometry, and non-BFC-certified geometry. The first set is rendered with back face culling enabled. The second set is rendered two-sided. An alternative (probably better) way would be to just create doubled up geometry (with opposite winding on the second copy) for all the non-certified geometry. Then, the rendering engine wouldn't have to care.
LDView keeps two sets of geometry: BFC-certified geometry, and non-BFC-certified geometry. The first set is rendered with back face culling enabled. The second set is rendered two-sided. An alternative (probably better) way would be to just create doubled up geometry (with opposite winding on the second copy) for all the non-certified geometry. Then, the rendering engine wouldn't have to care.