Thank you for the clarification David; that’s extremely helpful.
We have Panda’s main window embedded within a wxPython frame in our application. When we were using Panda 1.2.3, we did this with a bit of trickery in a DLL that we imported; now that Panda supports parent windows, we can use that system. But our old mechanism handled keyboard focus; the new code in Panda to support parent windows seems to interfere with our old keyboard focus control solution, a phenomenon that we are currently investigating.
Mostly, it’s the way we programmed things. Since Panda 1.2.3 didn’t send paranoid key-up events, we coded under the assumption that every key-up would be preceded by a key-down (i.e. our keyboard handlers aren’t necessarily all wrapped in binary-state switches; some handle all instances of key-up under the assumption that the corresponding key-down handler has already fired). This worked in 1.2.3 (though we suffered from the problem of sticky keys that I believe the paranoid send fixes; we’d been working on addressing that issue). So basically, it’s just on us to address this design change and fix our code 
Thank you for the help!
-Mark