Right rear brake dragging LONG

Hi,

I have a brake problem with the right rear brake.
I'll try to give as much info as I can.
The pads drag on the rotor causing to make it extremely hot, i can smell the brake when I'm stopped at a traffic light etc.
The brake doesn't always drag. It occurs at about 50 % of the drives I take.
it doesn't occur after hard or soft braking,there is no type of braking that seemes to bring it on.
The brake pedal is very high so not much free play.
When I aply the brakes they seem to work perfectly the pedal feels hard.
I've recently replaced the pads because i thought the problem could be related to this,no change but I noticed with replacing that I couldn't push the pistons back into the callipers.I had to bleed the calliper to push the pistons in.While bleeding the pistons could be pushed in easely and without and rough spots.
The rotor looks in good shape,not warped just a little bit grooved.
Could it be that the brakepedal doesn't have enough freeplay so that maybe the brakefluid can't bleed back to where ever it has to go back to ?
Any help greately apreciated,and please be as detailed as you can on how to fix this.
Sorry for my bad english too. I'm in the Netherlands