Hmm, it actually works fine for me. I compiled the code on Linux and I can push around a sphere with a sphere that is being controlled by the mouse.
Note that has_mouse() will only return 1 when the mouse is inside the window.
For what it’s worth, I recommend using Panda’s dcast mechanism for dynamic casting, which uses Panda’s typing system rather than relying on RTTI:
MouseWatcher *mouseWatcher = DCAST(MouseWatcher, mouseNode.node());