Tried with a couple of games (Ishar, Catacomb Abyss) and the problem keeps happening: the cursor keys work correctly when running dosbox under X, but not Wayland.
Other keys seem to work fine, although I haven't done any extensive test.
If this is a problem with SDL 1.2, then it's another more reason to push for 2.x as more major distros have/are transitioning to it.
Can be fixed by setting:
usescancodes=false
in dosbox.conf