Partial front brake seizure

The last 2 times I took my 1988 928S4 (32,600 miles, automatic transmission) for an extended drive (30 minutes), the following has happened:
1. Drive the car awhile (20-30 minutes), brakes are working fine.
2. Stop at grocery store or stop to get gas.
3. Restart the car and notice some resistance to movement. i.e., normally when I put the transmission in drive or reverse with my feet off of both the brake pedal and accelerator, the car will slowly move on its own. But, not now. It won't budge. The brake petal is very stiff and barely moves.
4. I drive awhile (35 mph) and notice the slight resistance to movement. The brake petal remains very stiff. When I take my foot off of the accelerator the car starts slowing down noticeably more than ususal (even while going downhill).
5. I stop the car and check the wheels. The front wheel rims are too hot to hold my hand on, but the rear wheel rims are just a little warm to the touch.
6. I restart the car and now the resistance is gone. The brakes are working
better, however they are now more spongy with the brake pedal going almost to the floor.
7. I drive the car the next day for a couple of miles and the brakes work fine. (Though, I didn't try the stop and start as above).
8. The next time I take the car out for an extended drive, the same 1-7 occurs.
What's causing my brake problem?

Rebuild the brake calipers as you probably have a stuck piston...

when was the last time the brakes were maintained? was the fluid flushed? if so how and what fluid did you use?

One possible cause is a maladjusted brake pedal, causing the rear cup to cover the fluid return port at the rear of the master cylinder bore. This prevents warming (thus expanding) fluid from returning to the reservoir, but instead self-applying the brakes, which causes more heating, which causes more self-application, and the cycle continues.

If you don't have one yet, then go to Home Depot or Lowes and buy an IR pyrometer. They cost about $25, and you will use it all the time around the house. If you have one, drive around a while and record the temperatures. I will then go and drive my own car around town and stop and record the temps of the discs and post it here. Wally is certain to be right- Get into your WSM's and adjust the clevis pin on the brake pedal.

N