Odd delete key behavior

This affects my X11-based desktop environments. I’m currently using Plasma (Wayland) to get around it, but there are a few features I really really like that I can’t get working in Full Wayland, such as Compose Key and kwin4 tabbed titlebars.

Starting after a zypper dup perhaps a week ago, my delete key began behaving oddly. In Konsole and in vtty1, it acts as one would expect, removing the character that the cursor is on, and shifting everything after it to the left. But in graphical applications (both KDE/Qt-based and Gtk-based when run in xfce), pressing delete will insert a strange box character, sometimes with “007F” (oh hey, that’s unicode for delete!) printed in the box, which will disappear at the next keypress or click to another window, depending on circumstances.

At first, I thought this was because I moved my Compose key to F12 (it used to be set to the Menu key, but my new laptop ditched that key), which is at least in physical proximity to the delete key. But undoing that changes nothing.

I can survive, however unhappily, in Wayland without tabbed titlebars — Compose key works in “Plasma (Wayland)”, though not in “Plasma (Full Wayland)” — but I’d appreciate if anybody had insight on what I might have done to wreck this key. My work machines are dupped to the latest tumbleweed and similarly set up but do not express this behavior.