Upgrade Exceptional to Elite failed

hi,
I just upgraded Vamp Gaze to Elite version, i went from 252 armor to 200 armor.
WTF is that?

It did not fail.

Grim Helm has a base def of 60-125

Vamp gaze automatically has max base def +1 with 100% ED (so 126x2 = 252).

Bone Visage 100-157

Upping rerolls the base def. You got a bad roll upping (well, the worst possible it seems).

Not a bug, Def overlaps between the tiers. A high roll on a lower tier can be better then a min roll on the next tier up.