Testing a bit more with the current beta running in window mode. For what it is worth.... and not worth fixing, one could even argue showing the splash screen on the second monitor is a feature
When display setting for the second monitor is set to "display screen saver on this monitor" clicking on the same icon to start a second instance brings up screen capture 1. But, when this is done the second and subsequent times without rebooting, on the first occurrence one gets the MA splash screen.
When the display settings are set to "show nothing on this monitor" one gets screen capture 2 (the splash screen).
The second instance is also the active window.
In full screen mode the results are what one would expect, as in when "show nothing on this monitor" is selected one gets a black second screen.