I think that it has something to do with BatteryDoctorPro not killing the app when it kills all running apps, or something like that, but I do not have that tweak so I cannot say for sure. I just remember someone else on this forum wondering what that icon was and a couple of people saying that is what it was. If it bothers you I think you can go into BatteryDoctorPro's settings and take it off of the whitelist.