Wikimedia Bugzilla is closed!

The use of the "subst" feature reproduces a source page's "include" contents without attribution.  Since the source is likely subject to GFDL, attribution is required.  One way to handle this would be to have the server enter a second entry into the target page's edit history when the subst is carried-out; "GFDL attribution: previous edit included contents SUBSTed from <source>".  This would satisfy GFDL.