I'm using Zotero 1.0.7 and if i export and entry as BibTeX the result is the following:

Original URL:

http://www.google.com/patents?id=_84lAAAAEBAJ&dq=Apparatus+for+automatically+setting+over-driving

Exported URL inside bib file:

http://www.google.com/patents?id=\_84lAAAAEBAJ\&dq=Apparatus+for+automatically+setting+over-driving

The exported appends a backslash ("\") before any special character (_, &, %, ...) changing the URL.

This change is required in BibTeX in the title and author fields but I guess that is not required in the URL field (I'm not sure of that).

See http://www.michaelshell.org/tex/ieeetran/bibtex/
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Q: Should I escape special characters (such as _ and %) within the url field of my .bib database entries?

The overwhelming consensus among TeX gurus is not to escape these special characters, but to enter them as-is in conjunction with an external URL package such as url.sty or hyperref.sty.
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Could it be possible to fix it?

Best Regards and congratulations for this great tool !!!

Chip