Description of the issue:

Client crash on hoovering over revolver in engineering workbench, after attaching bayonet. 100% repeatable.

Crashlog:

https://pastebin.com/fzNgVTU4

Versions & Modlist

Forge: 32.00.66 (Server and Client)
IE: 0.16-106
Optifine, other Mods and Resourcepack disabled

Fixed for next release

Attribute maps are immutable now, apparently, so we'll have to move over to the map builder here.

I'll look into this.