Its not game crashing no. But it is game ruining yes. Losing your armor to non armor damages is quite game breaking in many standard play aspects. And had it been detected earlier by someone and not me 94 versions later you wouldn't be so facetious. On top of that 1.11.2 is still a supported version soooooo
Latest log from 13.20.0.2307 test enviroment https://pastebin.com/fkSNbzqC
Outline: All damage sources do durability damage to armor.
Research:
I noticed a couple of mods had situations in which they were damaging player armor and so reported these to the mod authors. (in particular Tough as Nails and Blood Magic)
Both active authors told me that they used DamageSource.generic which makes use of bypass armor.
Out of a hunch I thought that it may be a forge bug.
So I tested by creating minecraft profiles with forge installed from 1.8 through to 1.10
When I noticed that these all complied with bypass armor I started testing 1.11 forge versions.
I tried a great deal of different versions until I pinpointed the issue starting in 13.20.0.2307. The bug affects all versions greater than it.
The test method was to
1.create a world.
2.equip a set of armor
3.throw a instant damage potion at my feet.
I did this with each forge version I tested until I pinpointed its origin at 13.20.0.2307
Note: This also occurs some time into 1.12 but is fixed by 14.21.1.2413 I have not thoroughly tested the 1.12 forge versions.
Edit: I pinpointed the 1.12 fix of this issue to 14.21.1.2394 by using the above method.