XWin and -multiplemonitors works once, but not twice?

[Jean-Claude Gervais]

When I run XWin with the following:
start /B XWin -engine 1 -nowinkill -multiplemonitors -nodecoration
-rootless -clipboard

It does open and span both my monitors.

If I close XWin and start it again, however, it only displays on the
first monitor.

The log file claims that both monitors are not running at the same
resolution/bit depth. This is untrue.

Any ideas why this might be happening?

Thanks!