It IS a bug if other buttons do work, especially for people who really need it (its similar to a button missing its caption for people with usable eyes or text using the same color as the button... one would see that as bug right?). Normal buttons do work out of the box, so its a genuine bug fix request, probably combined with a feature request asking to pay a little attention to usability for people with vision problems. Although I know its a small team, raising awareness is good.
It takes more energy and motivation to program in such situation because of all road blocks. Impressed. Its like magic
Its not only about eye problems too btw. Keyboard navigation should also work intuitively for people with movement issues for example. Easy to overlook when one doesn’t experience those issues one-selves, so good it gets some attention. Many times also easy to make it a bit more usable for those.