>> Here's the Lisp backtrace:
 >>
 >>    "select-window" (0x82a508)
 >>    "window-max-chars-per-line" (0x82aae0)
 >>    "window-adjust-process-window-size" (0x82b0a0)
 >>    "window-adjust-process-window-size-smallest" (0x82b618)
 >>    "window--adjust-process-windows" (0x82bbc0)
 >>    "redisplay_internal (C function)" (0x0)
 >>    "message" (0x82cdb0)
 >>    "progn" (0x82cff8)
 >>    "if" (0x82d198)
 >>    "let*" (0x82d3c8)
 >>    "catch" (0x82d608)
 >>    "fracy-display-frame-list" (0x82d7c0)
 >>    "if" (0x82dac8)
 >>    "fracy-flash-window" (0x82dc80)
 >>    "let" (0x82e018)
 >>    "ad-Advice-handle-switch-frame" (0x82e4a0)
 >>    "apply" (0x82e498)
 >>    "handle-switch-frame" (0x82ebe0)
 >>    "funcall-interactively" (0x82ebd8)
 >>    "call-interactively" (0x82f030)
 >>    "command-execute" (0x82f628)
 >>
 >> The C portion of the backtrace below selec t-window is this:
 >>
 >>    #0  redisplay_other_windows () at xdisp.c:597
 >>    #1  0x010aa09e in select_window (window=XIL(0xa000000006919aa0),
 >>        norecord=XIL(0x3d36a14), inhibit_point_swap=false) at window.c:540
 >>    #2  0x010aa62a in Fselect_window (window=XIL(0xa000000006919aa0),
 >>        norecord=XIL(0x3d36a14)) at window.c:628
 >
 > To clarify: these backtraces show where windows_or_buffers_changed is
 > being set to the value of 2, which causes us to retry redisplay.  It
 > is a direct consequence of the fact that window-max-chars-per-line
 > calls select-window.

If I replace the line

   (with-selected-window (window-normalize-window window t)

of 'window-max-chars-per-line' by the line

   (with-current-buffer (window-buffer window)

the problem persists.  So it is not the 'select-window' call per se
that causes the trouble.  The problem is with having that separate
frame that gets its echo area resized.  I'm not sure what causes it
but I suppose it's 'window-configuration-change-hook' itself that
selects that frame for running the hook.

Using 'window-size-change-functions' (patch attached) instead of
'window-configuration-change-hook' fixes the problem here.

martin