My 1985 spider has always had an issue of the parking brake handle coming back up from where it should be when the brake is released.
I was under the car and noticed that the part that adjusts the brake on the main cable was broken.
I bought a new cable and installed it and it still does the same thing. It is like the cable it too long and pushing the handle back up.
I have adjusted it all the way to take up as much slack as possible in the cable and it still acts like the cable is too long forcing the brake handle up.