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I omitted the first 4 casts of Disintegrate from the above log, sorry.

They look like this:

castspell: cnr96 spl405 (Disintegrate) vis0 x23 y15 spldmg999^M
vis 0 xvis 0^M
blastsqr: unr363 x23 y15 aoe0 dmg999 eff2 spc1082151040 as10186 al9^M
  affectvic vic364 hv0^M
hitunit 363 364 dmg999 spec1082151040 ba2^M
  spec_mr pen 13 mr 18 (unr 363 vic 364 dmg 2 eff 999)^M
   resisted^M

It's the Fallen Angel with MR18 passing the MR check against Disintegrate (cast by an Eye-of-the-Void wielding MR12 Maker of Heroes). The first resistance roll is made by the unit with Blood Vengeance. If it passes the check, nothing more happens, since there was no damage taken.

But when the unit with Blood Vengeance fails the MR check, then the Disintegrate caster still gets a chance to avoid the reflected damage, and if that happens, the BV unit dies:

castspell: cnr94 spl405 (Disintegrate) vis0 x23 y16 spldmg999
vis 0 xvis 0
blastsqr: unr316 x23 y16 aoe0 dmg999 eff2 spc1082151040 as10186 al9
  affectvic vic317 hv0
hitunit 316 317 dmg999 spec1082151040 ba2
  spec_mr pen 13 mr 18 (unr 316 vic 317 dmg 2 eff 999)
damage 996 on Angel of Fury, spec0x40805080(missile) ba2

The roll versus mr 12 does not show up in the log, but it's there because sometimes the damage reflection works and the Maker dies (my post above) and sometimes it doesn't and the Angel dies (this post).

I tested with:
Disintegrate caster = Maker of Ruins, Eye of the Void (pen+2, mr 12)
BV target unit = Angel of Fury, Flesh Ward (mr 18, bv 4)