I use a gamepad and the run state often gets stuck. That is, the "button release" event is sometimes missed -- most often when something causes the game to hitch, like the world-save. This is a bug, and perhaps it's also possible to occur with the keyboard as well. I can unstick it by tapping the run-button a couple of times.

It also seems like I can get double-run, if I'm stuck in run (with button released), then press-and-hold the button again, I zoom around extra fast. It's a little hard to control and "not what I want" when it happens, so I reflexively tap the button a few times to clear the state and haven't really explored or exploited it.