I have seen where this same issue has been resolved for other SCM plugins, but this is still happening when using the Repo and GIT plugins

When using the Email Ext plugin and selecting the "Send To Committers" option on failure, it appears that the committer user's full name is being used and is creating two email addresses to be sent notification.

For example if the committer user's full name is John Doe and the default email suffix is "@jenkins.com" then the committer designated emails are incorrectly being sent to:

John@jenkins.com
Doe@jenkins.com

The committer's actual email address is not even being accessed

Jenkins 1.472
Email-ext 2.22
Repo 1.2.1
Git 1.1.21