If I set the "Key(s) to change layout" to "Left Win" and "Right Win" in Keyboard Preferences->Options..., the window grabbing key is apparently interpreted as "<Super>Print". That is to say, having those (or either?) keys checkmarked in Options..., the window grabbing works, but by using either the left or right windows keys on my keyboard plus the PrintScreen key.
Unchecking those two keys in the Options... dialog disables this behavior.
The weirdest connection just appeared:
If I set the "Key(s) to change layout" to "Left Win" and "Right Win" in Keyboard Preferences- >Options. .., the window grabbing key is apparently interpreted as "<Super>Print". That is to say, having those (or either?) keys checkmarked in Options..., the window grabbing works, but by using either the left or right windows keys on my keyboard plus the PrintScreen key.
Unchecking those two keys in the Options... dialog disables this behavior.
I have no idea of what's going on here.