It appears that this plugin has stopped working with the newer versions of WP.

https://www.ads-software.com/plugins/stop-pinging-yourself-for-wordpress/

I just installed this on a WP 4.2.1 and ran two test posts linking to older posts on the same WordPress using the link interface with the search form for existing content. Both posts sent a pingback that creates a “this post was mentioned on bla” comment on the old post. So this plugin does not seem to do what I expected.

https://www.ads-software.com/plugins/stop-pinging-yourself-for-wordpress/