He doesn't get this on other forums he frequents, and he doesn't get it with Firefox. I have had no other reports. I've been using the same version of Safari/Mavericks myself and no problems. 7.0.1 (9537.73.11)
He has tried deleting the Safari preference file but that didn't help.
I assume this may be difficult to troubleshoot, but I wonder if anyone has any idea what can be causing this?