Auto-complete issue in Send Page by e-mail

steps to reproduce:

• login
• click on send page by e-mail
• start typing the name of an user
• auto-complete will kick in-
• do not write the entire user name and press return key
• you will see that the value in the filed won't be the full auto-complete suggestion, instead, it is only what you have typed.

This generates an error like: "The message could not be sent to sori: unknown email address."
User "sori" does not exist, autocomplete should have put "XWiki.Sorinello" instead.