Yes, I've had similar experiences over the years with various cars (each had 4 wheel disc brakes), and not my 560.
What i think you will find is your car has either a sticking pad or caliper. That is the cause of both the smell and the brake pedal going to the floor intermittently as you describe.
Take the car for a drive (not extended) and get out on the highway for a few miles. When you stop the car in the parking lot/rest area, hop out and walk around the car - feeling with the back of your hand the relative temperature of each wheel. They all may have warmth coming off them, but the hottest one is the culprit. If you can smell the brake, all the better, as it makes for a quicker diagnosis.
The reason the pedal goes away & returns later is that the brake fluid is getting hot enough to boil due to the fact that the pads are pressing on a disc, generating heat... even though your foot isn't on the brake pedal.
Replace the offending unit & the pad set, ck the discs for heat distortion, replace if necessary, flush out the old brake fluid.