Upon further testing, I found that the following:
1) problem happens when using NXFree with NoMachine client
2) problem happens  using plain X11-Forwarding when the app window is dragged to a second monitor
3) problem does not happen when using windows X2GO client.

I guess this is an XQuartz bug then.  Any guidance on capturing logs to submit to XQuartz project would be helpful.

Thanks in advance