I have a 1993 Beretta. Recently I noticed the brake fluid was low. Filled it up and after a couple weeks, it was low again. I took all the wheels off to look for brake fluid, found the passenger side rear wheel had a leaky wheel cylinder.
I ended up replacing the wheel cylinders on both sides of the rear tires. I re-used the same pads and drums, as they looked OK. I did get a new spring kit though, and then bled the brakes.
Well, now SOMETIMES when I step on brake pedal, the rear drivers side wheel kind of locks up. But it doesn't stay locked up. When driving down the street and then applying the brake pedal (without taking foot off pedal) the wheel will lock up (skid just a little) then act "normal" then lock up again, act normal, then lock up again... until the car comes to a stop.
I have tried to go down the street at about 20 MPH (shift car into neutral) and then apply the emergency brake and it pretty much does the same thing. So I don't think it had anything to do with the wheel cylinder or hydraulic pressure. Thanks for any input.

The brake shoes may have gotten contaminated and should probably be replaced.
Also, it seems that the rear shoe adjustment isn't even from side to side. Many brake or repair shops will do a free brake inspection for these items. Call around and ask what, if any, charge for the inspection. Then go see what they come up with.
I hope this helps.

It could also be as simple as a faulty or improperly installed spring. Recheck your work to be positive.