The Bay Area Masquerade

I've got a PM in my inbox that says there's an attachment on it. When I click on it, there are no attachments in it. This seems to have only happened in replies and forwards and not the initial PM.

Can you give me steps to reproduce? I can see if I can figure it out.

So, I've thus far had little success in attaching files in a PM. I tried sending a PDF to several individuals who have not received it. Followed steps of new pm, I selected the file, clicked add the file. I didn't put any commentary. No files were sent.