After a holiday of two weeks and leaving my 850 standing in the rainy Dutch wheather, I have a bit of a problem with the breaks: The front left break disk heats up disproportional,and the wheel jamms slightly.

After the holiday,at first the car would not move. I never use the handbreak, so that was not the problem. I was ready to get out of the car to see if someone had blocked the wheels, but tried one more time. The car kind of "broke free". Immediately after, when applying the breaks, they felt shaky. Kind of on/of, but the very fast. I never had the feling I could not break. Maybe it was not on/off, but 50-80% intermittendly break power.
I blamed this (and the car being stuck) on my presumption that the disks probably were corroded heavily except for the spot were the pads had rested. I thought this problem would go away and indeed it grew less and less. After about 100km it was gone.

After about two weeks with several short trips and two longer ones (100km -500km) with no indication of any problems, it was by coincidence time to change tires. The mechanic then noticed that the front left wheel was kind of stuck and that the disk was quite hot.
After the disk cooled down, the wheel could (as far as I could see) rotate without extra effort. Also when driving at whatever speed, I notice nothing in steering breaking, etc. However, the disk of the wheel in question does heat up more than the others (tested by appying some water on the disks).

Now the big questions: What is it and how can it be helped?
I it slightly stuck calipers?
Has the disk bended?
Excessive build up of break dust?
other suggestions?

Looking forward to your insights.