How are you selecting sending a PM. On this new iteration of the forum it appears you only need to click on the name of the person you want to PM. That will open what appears to be a normal message box but aimed at the PM person not the forum.
I just click in the top of the PM box and hit my enter button 3-4 time to create space. Then I click back at the top of the box and type reply. This will give you some room to work and keep things separated and neat. Don't know if this is the correct way but works for me.