Dave:
I was able to reproduce this bug by mirroring a wall with a labeled door, using the
Label Door-Marker 15. There is code in the label for
Wall_Direction that I think is supposed to correct for this. The only solution I found was to change the Label Rotation value (Label Settings > Symbol Label > Rotation Angle) to 90.01˚ (setting this to 90˚ does not work correctly).
It would help if you named the Label you are using, as well as added screen shots of the problem.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David