wxPython and Panda3D both have a main loop, and both want to own it. If you use Panda’s wx integration, it uses Panda’s main loop, which means that Panda has priority and wx is a slave to Panda’s whims. If you want wx to have the upper hand, don’t call run() but instead use the wx main loop and call Panda’s taskMgr.step() in a wx task/timer/whatever it’s called.
More explanation:
panda3d.org/manual/index.php/Main_Loop