When using Colemak layout, which remaps Caps Lock to function as Backspace, as non-default layout Caps Lock ends up working as both and doesn't auto-repeat as Backspace. If Colemak is the default layout, Caps Lock is also overriden to function as Backspace in all other layouts. Gnome apparently [url=https://forum.colemak.com/topic/287-backspace-is-caps-lock-and-backspace/]has an identical problem[/url]
Just in case, the OS is Arch Linux.
Never mind, it's probably a X.Org bug.