It's weird.  I vaguely remember something about this being fixed
ages ago and thus the hack being removed from the distrib/i386
makefiles but I can't find anything about it from mail-index.netbsd.org

anyway, the fix seems to have rotted -- i can no longer build
a working i386 bootfloppy unless I put the hack back into the makefiles.

Oddly enough, the problem seems to be less noticeable in single user
mode.  And running a non-UVM kernel didn't seem to help either.

I'd file a PR but I have no idea what to write into it ...