Armor (and saves) set to NaN

[velius]

Character is a cornac marauder, antimagic, with no chants. Started in 1.5.0, error occurred in 1.5.0 and in 1.5.1 when upgraded. I reloaded a backup save and it occurred again at around the same point in character development (right around the ambush after dreadfell). If requested I could also upload a save that appears to not have the error if that would be helpful.

Here is the save:

https://www.dropbox.com/s/5amv4nsq3yzus ... n.rar?dl=0
and an unbugged backup save:
https://www.dropbox.com/s/pf6md5mwapw5y ... p.rar?dl=0

As for the .log information:
Lua Error: /mod/class/interface/Combat.lua attempt to perform arithmetic on field 'combat_armor' (a nil value)
At [C]:-1 __add
At /mod/class/interface/Combat.lua:1292 combatArmor
At ...ns/ashes-urhrok/superload/mod/class/interface/Combat.lua:24 field
At /mod/dialogs/CharacterSheet.lua:465 compare_fields
At /mod/dialogs/CharacterSheet.lua:1108 drawDialog
At /mod/dialogs/CharacterSheet.lua:222 switchTo
At /mod/dialogs/CharacterSheet.lua:56 on_change
At /engine/ui/Tab.lua:93 select
At /engine/ui/Tab.lua:54 fct
At /engine/Mouse.lua:58 receiveMouse
At /engine/Mouse.lua:98 delegate
At /engine/ui/Dialog.lua:754 mouseEvent
At /engine/ui/Dialog.lua:485 fct
At /engine/Mouse.lua:58

[darkgod]

Hum do you have any idea what happened that affects armour in between those two saves?