OK. I think I know whats happening.
on the breadboard with separate resistors on each button, when i press button 1 its voltage drops to 0, but at the same time buttons 2 and 3 drop to about 1.5 volts. the same happens with each button so when it is pressed the voltage drops, but not to 0.
on the perfboard, when I press button 1, or 2, or 3, the voltage on all 3 drops to 0. so it is like i am pressing all 3 buttons at once.
i assume that separating out each button with its own resistor is whats preventing the complete voltage drop on unpressed buttons on the breadboard version.