To add some information to some things that were said earlier:
I am basically certain that EM checks on "greater-than-or-equal to max hp" rather than "exactly equal to max hp" (such that you can and do EM at 104/100 HP). This can be seen sometimes when using liquid antimatter-type strategies (basically in unupped FG predictions these days), where healing occurs before the damage, and death check occurs before the line in the code that says "if {hp>maxhp} {hp=maxhp}". Sometimes EMs against those FGs will be worth 124 electrum or something similar when I have only 100 max hp.
I believe the root cause of the issue is rather that a death check was added after damage was dealt and before healing occurred.
My understanding is that this is one of those intentionally-coded things that kinda looks like a bug but is actually a rather roundabout way of preventing something that looks more like a bug (similar to refunds for cancelling activated abilities intentionally not happening).
edit: As further argument against 104/100 HP not being considered an EM, this would result in situations where (against a FG for example) the player would receive 60 (or 61) electrum at the end of the battle. I have never observed this - when vampiric does not trigger, the game ends while providing ~59 electrum.
I believe the routine for resolving damage is something like:
(1) Resolve damage (with antimattered creatures being treated as negative damage, i.e. healing)
(2) Check for death
(3) Resolve on-attack effects (i.e. heal player by damage dealt in the case of vampiric, heal player by five in the case of staff, etc).
(4) Check for death
(5) Check for hp>maxhp, if so hp=maxhp
Not certain what order 4 and 5 are in, but I suspect that what happened is that a death check was added any time any HP changes at all.
edit2: FWIW, from a standpoint of whether or not these features are desirable, I think this particular change is more or less in line with the previous situation where not all cards were resolved before death, such that you don't get a guaranteed EM from SoGs or bonds or whatever. If you want to receive the title of "elemental master" for a given game, you just need to ensure that you have full hp before you deal the deathblow. I wouldn't necessarily mind if it were changed to make EMs easier, but I don't have a whole lot of cognitive dissonance about it as it stands.
