This happens a lot (to my great relief) when I'm doing normal actions. It is the following: when my stamina runs out COMPLETELY, instead of reacharging 5 (per milisecond) points, it appears to recharge 100%. However, I've never encountered this bug at later levels, so I think what happens is that it recharges a crapload (> 3000) of points instead of 5. Maybe 5000?
Anyway, it's a benign bug and nothing gamestopping, but I just thought I'd point it out.
Happens when I use Swing, Crouch-Hide, normal running, anything.