Pages such as Wikipedia's page on Subversion produce invalid TeX output on the Special:Cite page; the % characters in the title must be escaped with a backslash to allow correct processing by TeX. This is confirmed to be the case with pdflatex program in the teTeX for Mac OS X.
OS: Mac OS X 10.4
Platform: Macintosh
URL: http://en.wikipedia.org/w/index.php?title=Special:Cite&page=Subversion_%28software%29&id=121928089
Escaped URL is not compatible with URL handling packages such as url.sty and hyperref.sty. Since using such packages are recommended when url handling are required, the normal approach is to write out the URL as-is, and let the URL package deal with it.
I don't know if it is the same bug (the page linked isn't accessible anymore) but we have a strange BibTeX section code behaviour:
https://it.wikipedia.org/wiki/Speciale:Cita/Sottosegretario_di_Stato#BibTeX
Note that the code goes to a newline.
How to fix it?