It's a total non-issue. Normally the arms move independently and center according to keeping the spring tension balanced as they come to the rim. But spring centering forces are low, and easily thrown off with some friction or binding.
However the caliper functions like closing your hand to squeeze the rim between the thumb and forefinger. It doesn't matter that one arm touches first. Once it does, it stops moving, and the other continues until both are in contact and squeeze the rim between them.
No matter how it happens braking is always the result of the rim being squeezed between the arms.
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