Google Docs revealing email address

I just discovered a security hole in Google Docs:

When you invite someone for collaboration on a document and paste their non-Gmail-address into the invitation form, and the person has a Google account with that address associated to it as a secondary address, their Gmail address will be revealed on the following screen.

A real security hole if you ask me as you can use this function to associate real names (that may be part of the Gmail address) or other user names to email addresses you are researching into.