Only one "Mastery" support gem accepted per skill

Before 0.3 it was possible to support skills that were related to multiple elements with multiple "Mastery" support gems. Fire Mastery and Lightning Mastery on the same Skill, boosting it two levels e.g.

After 0.3 you can only support each Skill with one Mastery at a time, i.e. either Fire or Lightning Mastery, either one is fine but not both.

This looks like a bug to me because skills like Unbound Avatar don't even offer as many support gems as they have slots to fit support gems in the late game. It used to be the only viable support gem setup to have multiple levels of Mastery socketed into the Unbound Avatar - after having the new freedom to put each support gem on every skill at the same time, it seems I have the freedom to have open support gem sockets on my Unbound Avatar in the late game, because there is no content to fill the gaps.

I mean, I can't imagine this was a silent Unbound Avatar nerf, since nobody complained about this non meta skill - didn't find anything in the patchnotes either.

+1 Infernal Hound is a sad dog

We can add this to the growing list of supports that don't work with internalist minions

All such support gems share the same category – "Mastery". You can't socket multiple supports of the same category into one skill.