I'm trying to use lightmap from model-combined-deferred shader for a cockpit panel now.  There's a 3D model of an attitude indicator that partly sits behind the panel.  Yet the panel itself has no hole cut in it for this instrument, instead panel texture has transparent region to make attitude indicator visible (the texture: https://github.com/kroki/tu154b/blob/future/Model/vc02_t.png).

Now when I apply model-combined-deferred (and I also tried -transparent) to the panel those parts that were transparent before are now visible as a white area, see http://hostingkartinok.com/show-image.php?id=efab318e4c09b484dbd3bd9f80864f04 .  My wild guess is that Z-buffer doesn't honour alpha=0 in the texture (and I wonder how it should handle 0 < alpha < 1), though I can't figure this from the code.  Is there any way I can workaround this problem (not cutting the actual hole in the model, because the technique with transparent texture is quite common I think)?

Thanks in advance!

  Tomash Brechko