1994 Toyota Camry Stuck

Recently, I replace a brake line to my front, driver side caliper. After doing so, I accidentally put pwr steering fluid in the brake reservoir. I removed the fluid right away from the reservoir, bled the front caliper and all was fine.
Yesterday, after sitting at a stop light, the brakes would not release and the pedal was very stiff. After turning the car off, pumping the brakes, and then starting the car with the pedal fully depressed, they began to function properly. Is this an air in the line situation, bad fluid situation or worse