The spell Greater Magic Fang only seems to affect one summoned creature, though it does some times sound as if it does it multiple times on that one creature.
I'm not sure if that is intentional or if its supposed to work like Magic Fang and affect all summoned creatures, I just couldn't find any information on it anywhere. But I'd assume that seeing the lower tier spell affects them all, then the greater one should too.
Ghostii kindly found this:
: GoD1x, "Magic Fang and Greater Magic Fang, when used by clerics with the Reptilian domain, will affect summoned creatures."
Which is a domain my character has.
I'm not sure if anything's been done to this yet, but it now did it on two of my 4 summoned creatures when I tested it earlier today.
From what I can recall, it's been changed so that it enhances 1 creature per 3 caster levels. It may be not a bug but rather an undocumented balance change.
I would just like to say thay my player tool from the Sorcerer Perk "Cultist" that grants Magic Fang (5) 1/day grants it to all of my summons. All 12 of them. Rather, the spell special effect is played on all of them, I am unsure if they all receive the +1. But I will investigate it.
The bug report in question relates to Greater Magic Fang, and not Magic Fang.