I certainly can't rule out the possibility that the 35mm, MF, and larger formats use different emulsions. Another possibility is that grain size is interacting in odd or exaggerated ways to developers and/or degree of development. The most extreme example I've seen of this was some 35mm Svema FN64; developed in Rodinal, DS-12, or PC-Glycol, grain is similar to that of Efke KB50, but in XTOL, the Svema's grain is horrific. That's a very odd thing, really, since XTOL has a reputation as a grain-reducing developer, but it has the opposite effect with Svema FN64, at least in my experience.
That said, the D-76 I used for my one roll of Efke KB100 is common enough that I wouldn't expect it to cause problems with any film. XTOL is probably newer than the Svema FN64 emulsion design, and I doubt if Kodak made testing XTOL with Svema films a high priority when it created XTOL, so a bad reaction with that combination is more understandable.