There are those strange formations in at least one Morlovia battle (was doing advanced 17 when I spotted it) where boss is standing behind multiple minions.
When I used Proteus’s special on boss (it should hit boss and adjacent enemies) it affected everything.
I don’t have any other reasonable heroes that hit 3 targets to check whether they also hit everything. But even if it’s only Proteus, it still sounds like a bug (unless that’s a feature related to this particular formation).
Just in case: the particular chain of specials i used is: Wilbur, Boldtusk, Proteus, Sonia - so damage sharing on enemies got dispelled by Sonia. But you can see Proteus’s special on everything. And it’s not just a visual bug, every minion was getting DoT in further turns.
It’s a feature. Since these formations are unavailable to players, they can reward players who bring splash damage heroes even if it makes them a little OP. I use Musashi and GM on seasonal events for the very reason.
Definitely made my day when I saw this myself while playing morlovia on normal. Little more bang for the buck with my characters that only splash 3. Curious as to advanced morlovia. Scared as hell to try it as my 4* team is not incredibly strong and not much depth to 4* (six or seven, can’t remember off hand) or 5* (none) characters.