Small update - I tried 2 things yesterday on 2 systems I had at hand: -I tested on a NetBSD 6.0 amd64 box with a local X server and SDL backend - that showed the very same symptoms as I saw before. -And on a Raspberry Pi with NetBSD 7.99 (current) arm - also with the same issues. I tried both SDL rendering on X as well as on the console (wscons). Good news there is that gdb is working as expected, so I will be able to debug this further.