Nikon D3 viewfinder weirdness

I ran into a really strange phenomenon today—while shooting the Zeiss ZF 28/2 Distagon with the sun positioned in the upper left of the frame, I noticed an small, but intense fireball in the lower right of the viewfinder, clearly a derivative of the sun itself, but much smaller and more focused.

Since the actual image shows outstanding flare control, it’s clear that the issue lies with the D3’s viewfinder optics, or possibly some interaction with certain lens(es). I’ve never before seen a problem like this, and it’s disconcerting. I reproduced the problem again later under somewhat different lighting conditions with a less intense result. I don’t yet know if it’s something peculiar to the D3 and the 28/2 Distagon, or a general problem, and I haven’t yet tried the 28/2 Distagon on the Canon EOS 1Ds Mark III.

Update: Looking carefully at the resulting image, the “fireball” does seem to be in the same place in the frame as seen in the viewfinder, but the ZF 28/2 Distagon’s flare control supresses it superbly. Perhaps there is some focusing screen interaction. Once understood, the problem can be ignored from an intellectual basis, but still the visual feedback remains disconcerting.