The Words "Pin It," A Copyright Infringement?

Has istockphoto declined this image
in fear of infringing on Pinterest's trademark?

An istockphoto contributor has reported that one of his images was refused by the photo licensing site:

A few days ago I received a message about was deactivated a photography file with the phrase "Pin It" written in a paper. [...] I really don't understand why the phrase "Pin It" creates risk of infringement of copyright

A representative of the agency was cryptically tight-lipped about the reasons:

You'll be better off talking to Scout than you will the forums. [...] Please open a support ticket for further assistance.

Whoever knows what role Pinterest has, or doesn't have in this, isn't talking.