Specifically, it says:

Warning: unable to close filehandle properly: Bad file descriptor, <STDIN> line
        21 during global destruction (#1)
    (S io) An error occurred when Perl implicitly closed a filehandle.  This
    usually indicates your file system ran out of disk space.

This happens with (as far as I can tell, I haven't tested exhaustively) all
command-line yast invokations that involve a module. So, e.g., "yast users
help" or "yast sysconfig help" will produce this message. "yast help" on its
own, however, won't.

It does not appear to affect yast's exit code, or it's ability to do its job;
if I run "yast sysconfig set LOADER_TYPE=none", it does the right thing and
then produces that message while exiting.

Despite the hint that it may be space-related, this happens on multiple
computers, all of them with plenty of space available on all filesystems. These
systems are all running recent (~2 weeks) versions of Tumbleweed.