On some bridges, if the balls are at an odd angle they will get "stuck" like that..
You need to hold them in place (and not let the string twist) and kind of guide them as you are bringing the strings up to tension.
On this bass for example, I have all the balls with the hole facing outwards... If they were facing side to side, they could slip into the bridge at an angle and get kind of wedged in there:
However on this bridge, it doesnt matter since they are just resting over a hole rather than a "slot"
