[Snake]

Backstab's not recieving damage bonuses. Only bonus present is from Flank.

Front (No Flank Damage, No Backstab Damage, No Backstab Crit)
Side (Flank Damage, No Backstab Damage, No Backstab Crit)
Back (Flank Damage, No Backstab Damage, Backstab Crit)

[Rendar]

It also appears that Armor Of Eyes isn't actually getting rid of the bonuses of Flank/Backstab.

[Neus]

What's actually happening is that Backstab is applying in all directions. This has been corrected.

If Armor of Eyes is bugged then make a separate bug report with details after you've tested it.