I no longer have PithHelmet.bundle but you got me thinking. I went to /Library/Application Support/SIMBL/Plugins and removed Saft.bundle. After quitting and relaunching Safari, the problem was solved. Even though Saft was not loaded when Safari launched (and a message to that effect appeared at launch), something in there was causing problems.
Thanks for the suggestion, dk!
As always, you have the memory of an elephant for these things. How do you do it?