- never mind then. lol
Hmm, I think you're referring to a Visitor Message (VM) not a PM.
I can get a reply box when I click on "Reply to Sender" on my own profile page, if a user sent me a VM.
If for instance, I click on "Reply to Sender" on your profile page (not my own) to see your VM from sorethumbs, I only get the that VM with no way to reply to it like you mention.
You can always just click on the users profile (just click on his avatar there on your profile page), in this instance - sorethumbs, and write your reply on his profile page as a VM. Not required to use "Reply to Sender" link.