It's certainly not intended, it's a bug.
What do you use to send your e-mails?
don't know what he's using but that's been reported by others already yesterday I think, on Gmail/browser. Thanks god I haven't experienced that, no webrep here, I would have gone mad
a question: do affected users use non-ssl sessions in Gmail (as that's still possible, even if not the default anymore)? ... yeah, I know there are non-encrypted elements anyway on Gmail pages.
On a side note, I rarely use Gmail browser interface, but when I do Google ads are blocked by AB+ ... wondering if they thought of including WebRep in their filters
(don't take that too seriously, I know you said there was a bug )