For fun, take a look at:
/System/Library/PrivateFrameworks/WebKit2.framework/WebProcess.app/Contents/Resources/com.apple.WebProcess.sb
FIXME and deny rules are one way to fix a "problem".
Log lines like this just might bug you enough to change platforms eh?:
sandboxd[124] ([363]): com.apple.qtkits(363) deny file-read-data /Library/Managed Preferences/user123/.GlobalPreferences.plist
Where the directory does not exist in the users home, but it can't be created either because of a deny rule in the sandboxd!