Just came across this thread. Yes, the problem with my 23mm Rodenstock was not camera-specific, nor was it lighting-specific. I would always get a big red flare spot in the middle of the image circle which would require extensive work in PS to remove.
Enda's telling of events is accurate - Rodenstock replaced the lens with another defective copy. Apparently this was an endemic problem with early versions of the lens, which has since been corrected. HOWEVER, they have not pulled the old lenses off the market nor are they capable of tracking which of lenses they have in stock are defective (as Enda said, Rodenstock told me they couldn't identify if it was a corrected lens based on the serial number).
There are good copies of this lens out there, but in good conscience I couldn't do business with a company so woefully incompetent as to behave in this way. Spend €5000 on a lens and you expect to be taken care of.
Arca-Swiss (who were the intermediaries in this as the replacement lens from Rodenstock had to go to them first for focus calibration and mounting) were excellent throughout. I got the Schneider 24mm instead, and while it doesn't have movements on the P45+, for most of the work I do that's not a deal breaker. If Schneider come out with a 24mm that has a larger image circle, I imagine I'll buy it, but for now I'm happy with the 24mm.
Rodenstock won't be seeing any more of my business.
Cheers,
Peter