[Tx Firefighter]

Swollen brake hoses guaranteed. I've seen it many times.

They swell shut on the inside. They'll pass the ultra high pressure from the master cylinder when applying the brakes, but the springs in the drums aren't strong enough to retract the wheel cylinders and force the fluid back through the restricted hoses when you release them.

If you want further proof, next time it does it, slide under there real quick and crack open the bleeder valves for a second. The fluid will squirt out under a lot of pressure rather than dribble or drizzle. It's the springs retracting the brake shoes that causes the pressure. You'll also hear the brake shoes relax away from the drum if you're in a quiet environment.