Why is this bug still present in March 2016 for Steam linux and CS:GO?
This issue should need the same debugging information requested by @rcgordon at https://github.com/ValveSoftware/Dota-2/issues/453#issuecomment-181218057. A libSDL2 dev also needs to get that information.
Will do this tomorrow. But from memory xev simply shows it is interpreted as an ordinary backslash.
Nothing extracted yet.
Source/GoldSrc games respond to the backslash keypress from American keyboards (where backslash is above enter) whilst binding keys in the Settings GUI. These same games do not respond to the backslash keypress from European keyboards (where backslash is beside left shift), meaning that the backslash key remains unbindable.
Tested on Day of Defeat Source (Beta) and Counter Strike 1.6 on 2 Arch Linux x64 machines, using an American PS/2 keyboard and a European (UK layout) USB keyboard.