I think this is a bug in 3.6.2 (eval copy):
1. Click "New Post" in toolbar
2. Paste something into Title: filed using cmd-v or right click->paste
3. The window will change its title, but the title field remains empty.
EDIT: This happens because the text I pasted had a linefeed at the end. Perhaps the lineedit should not allow linebreaks, or at least expand / show scrollbars if it happens.