Back in July, I posted a thread about lights hosting to reference planes UPSIDEDOWN here and here. I have wanted to post this fix for awhile. Reference planes have a top and a bottom. Light fixtures (and other objects) host to that "normal" surface. When you draw a plane from right to left, fixtures host correctly. When you draw them from left to right, the "normal" surface is up and the light hosts upside down... I guess in actuality the plane is upside down and the light is normal to it. Why host to a plane in the first place... well read the above links for more, but you could lose all of your work if the ceiling in a linked model is deleted and your hosted to it. However, it seems that has been fixed recently.
Anyway, enjoy my first JING video that tries to explain what happens.
Note: One of the issues in those past posts was that the System Family "Basic Ceiling: Generic" behaves like a reference plane. Unfortunately you don't get the chose how the ceiling gets placed in the model.
It seems that JING videos don't scale so I can't embed it. Follow the link.