Thumbs display shifts from Tmux

[nyarly]

I'm finding that when I invoke Thumbs, the text in my terminal moves around. It erodes the usefulness of the tool, because I have to stop and re-find the data I wanted to grab, which pulls me out of the quick flow that Thumbs engenders.

I suspect the issue has to do with counting scrollback lines in the presence of terminal formatting characters, but I haven't dug in to be sure.

Is this a known issue, or worth characterizing better?