Chalk another one up to user error.
I designed by button in separate view so that I could have a master copy in a library and just instantiate via embedded views wherever I needed it. And there was a parameter on the view that I could bind to a PLC tag for writing the command.
When binding to the PLC tag I ensured that the binding was bi-directional, but I overlooked that that the view parameter also needed to be bidirectional. Once I made that change the Mouse Leave event seemed to write the correct value.