sounds to me like a error in the false northing or something similar if it works for the dem and you double checked using the same settings for the ortho then it might be a bug.
try to convert into other system for export as temporary solution you should still be able to convert it back in a GIS software
frank
If I select "North Up" option on Geotiff, then the bottom corners of the export tile is what looks like the actual top corners, and if I do not check the "North up" option, it appears in correct position, but just upside down. I still need to remove the negative (-) sign because it's actually positive.
I hope if it's a bug, it can be solve fairly quickly, for most clients really wants orthophoto background on surveys.
Ill try to use another projection to see if it is the same result. Thank yo for the sugestion