Hello, I recently upgraded to Ubuntu 14.10 and ran into this issue; it does appear tmux is at fault (or rather, screen's terminfo description).
The tmux FAQ (http://tmux.svn.sourceforge.net/viewvc/tmux/trunk/FAQ) has an entry "vim displays reverse video instead of italics, while less displays italics (or just regular text) instead of reverse. What's wrong?" which describes a fix involving creating a new terminfo file. The only wrinkle for byobu is the "default-terminal" command should go in ~/.byobu/.tmux.conf instead of ~/.tmux.conf. I suppose this may be too much for byobu to fix automagically, but it does seem to be a head-scratcher for users who don't investigate deep enough to find a fix in tmux. HTH, Jeff
