When breaking lightly it doesn't happen, however when clamping hard it gets stuck. Whenever I bring the bike to a complete stop I have to manually un-jam it.
Here's a video:
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It looks like there's dirt in the hinge. When you brake hard, the arm reaches the dirty region and sticks there, and the spring can't force it back; when you brake more gently, it doesn't get into the sticky region. Detach that arm, clean it and re-lubricate it.
It happened to me once that a V-brake pad that sat too low relative to the rim's braking surface literally wedged itself down into the rim at braking. To alleviate this, reposition both pad's position and angle. Always make sure that it clears the tire, because otherwise braking friction will destroy the sidewall in no time.