Text messages jitter, run off right margin of screen

My text messages jitter irregularly, about once every ten seconds, sometimes a couple of line heights or so vertically, sometimes moving a similar or smaller distance horizontally, and sometimes in the word wrap (longer text messages often stop line-wrapping partway through, and changing the window width may or may not temporarily fix). One message was also are placed way off to the right of the bubble it should be in, running, like the unwrapped lines, right off the viewable screen. This makes it unreadable unless you can resize the window to be wide enough.

It would be nice if it only moved when there was something new to attend to, though I suppose having relative "30 minutes ago" timestamps makes that strictly impossible.