tmux / urxvt: Odd behavior when selecting text with mouse

I've just recently begun experimenting with urxvt as a terminal emulator rather than xterm. I'm a heavy tmux user, so having both work seamlessly together is a must.

I've noticed that when ruing tmux inside urxvt, there is some odd behavior when selecting text. I hold shift, use the mouse to select text, and the text is highlighted in yellow (as if tmux is still handling it) but then blinks and flashes to a black background -- almost as if urxvt and tmux are competing for control of the selection. Does that make sense?

In xterm, when I would hold shift and select text I would notice that it would highlight in reverse colors (as opposed to tmux's yellow background). In urxvt, the selected text still seems to be controlled by tmux.

Any ideas on how to fix this weird behavior?