[winswitch] Floating point exception when trying to start application on xpra display

[dan l]

I have a script called /home/dan/run-calibre on the remote machine, js1, that has the following contents:
#!/bin/sh
export QT_XKB_CONFIG_ROOT=/usr/local/share/qxkb
/usr/local/bin/calibre

I have an X server running on my local machine, and can start this application without issue by doing the following on the local machine:
DISPLAY=:0 ssh -Y dan at js1 /home/dan/run-calibre
*That works without issue.*
Then, I try to run this under Xpra. I start Xpra like this:
$ xpra start :101 --daemon=no --pulseaudio=no --mdns=no
2016-08-20 14:15:55,462 server uuid is 6f28c125f92b4f5b94c42f8526eacb4f
2016-08-20 14:15:55,642 no RandR support
** Message: pygobject_register_sinkfunc is deprecated (GstObject)
2016-08-20 14:15:55,972 using notification forwarder: DBUSNotificationsForwarder(org.freedesktop.Notifications)
2016-08-20 14:15:55,978 xpra server version 0.15.10 (r11439)
2016-08-20 14:15:55,978 running with pid 11255
2016-08-20 14:15:56,009 xpra is ready.

Then I try to start the application and get a Floating point exception:
$ DISPLAY=:101 /home/dan/run-calibre
Floating point exception
$

Nothing appears in the xpra log/stdout when I do that. The xpra server continues to run, and I can start other X clients (such as xeyes) on it sucessfully.

Any recommendations for how I can debug this?
Some other info:  * the application, calibre, is an ebook management application  * the application runs OK when the X server on the local machine is Cygwin/X started with: "startxwin -- +iglx -wgl" This is the non-Xpra case (that works) that I mention above  * the remote system is FreeBSD 10.3. I realize the version of Xpra on the remote system is not the latest (it is 0.15.10 r11439) but that is the latest as a FreeBSD pkg
  * the local system is Windows 10 using Xpra 0.17.4 (r12925)