Description:
Under some rare circumstances libpar2 will segfault. From a cursory inspection it appears this happens when par2 files are missing a verification packet.

Fortunately, thanks the the nzbget devevloper, a patch is maintained in the nzbget repository, "libpar2-0.2-bugfixes.patch"

I've applied and tested the patch. It enables libpar2 to handle (sucessfully verify, probably repair) defective par2 files and furthermore it does not interfere with normal par2 files. So I would say it works well.

The thread detailing the problem and the patch can be read at: http://sourceforge.net/tracker/?func=detail&aid=2986098&group_id=102632&atid=632376 and in addition I've attached the patch and the accompanying PKGBUILD here.

Since the parchive project seems to no longer be developed - last news update @ 2004, last release @ 2006, and both this patch and another submitted approx. 1.5 years ago without response - patching the libpar2 package in Arch seems the best course of action. These are the parchive sourceforge threads for both patches:
https://sourceforge.net/tracker/?func=detail&aid=2209433&group_id=30568&atid=399700
https://sourceforge.net/tracker/?func=detail&aid=2209488&group_id=30568&atid=399700

Additional info:
community/libpar2 0.2-3