I've never experienced that, but I'm the kind of guy that likes his brakes to work well and ALL the time!
I'm guessing that a component (piston) is sticking, either in the master cylinder or in one of the slave cylinders.
If it were my bike, I'd take it to a reputable shop and have the brakes serviced, because, with brakes, I don't trust my DIY skills beyond replacing the pads. It sounds like a good cleaning of all components and replacement of the fluid might well clear this up.