xfce4 window buttons missing proper xterm icon

I recently upgraded to 13.4 and my xfce4 desktop now shows squares instead of
the xterm beastie for xterms in the main panel buttons.
The launched xterms have the proper icon in the title bar.
Other apps like thunderbird, gimp, vlc, darktable, and xpdf show a proper icon;
but X apps like xcalc, xmag and xgc show the square in the button menu also.

Any ideas what's missing / messed up?

~$ ls /usr/local/share/pixmaps | grep xterm
filled-xterm_16x16.xpm
filled-xterm_32x32.xpm
filled-xterm_48x48.xpm
mini.xterm_16x16.xpm
mini.xterm_32x32.xpm
mini.xterm_48x48.xpm
xterm-color_16x16.xpm
xterm-color_32x32.xpm
xterm-color_48x48.xpm
xterm_16x16.xpm
xterm_32x32.xpm
xterm_48x48.xpm

The xterm.desktop file:

~$ grep xterm /usr/local/share/applications/xterm.desktop
# $XTermId: xterm.desktop,v 1.16 2022/09/06 21:10:14 tom Exp $
# this file is part of xterm
Exec=xterm
#Icon=xterm-color_48x48
Icon=mini.xterm_48x48

seems to be ignored; neither the commented-out xterm-color_48x48 nor the
mini.xterm_48x48 seem to do anything when active.

Thanks for any pointers,

Gary