I have a c-shaped side rail, which has a mirrored configuration. (mirror and body-delete/keep features)

The original configuration has a flat pattern derived configuration, which is sufficient for the drawing.  The mirrored configuration does not.

My problem is that the mirrored configuration keeps randomly going flat when in an assembly; the mirrored flat pattern becomes unsuppressed.

I don't want a mirrored part flat pattern, but I can't delete it.  Is there a way to make sure I don't have a mirrored part flat pattern?