The following files seem to be left over after running both 'make clean' and 'make distclean' on GTK+:
jbg@rhea:~/Projects/WebKit$ svn st
Particularly DerivedSources causes problems for me, with strange KJS errors after rebuilding after doing 'make clean' and 'make distclean'.
*** Bug 18332 has been marked as a duplicate of this bug. ***
Closing as the fix for this bug was landed in http://trac.webkit.org/projects/webkit/changeset/32257.