The indicator blinks between what looks like an empty graph (in a vertically shorter box) and the actual graph (in a full-sized box). This is best demonstrated in a video so I’m attaching one below.
Both the official repository version (0.4) and the one from daily PPA (0.5) exhibit this. Different color schemes don’t seem to affect it (i.e. the problem remains). There’s further problems when I add a third graph, but this report is just about the blinking.
(Bug #1336828 is about the indicator missing entirely in 14.04, so I decided to report this slightly different issue separately.)