The mode only rewrites the seed after a queue, so the first queue after
switching from Fixed to Random reused the last seed and ComfyUI returned
the cached result. Entering Random now rolls a new seed right away, and
leaving Fixed for Step takes the first step; flipping Step's direction
leaves the number alone. Checked live on a CPU instance: a Fixed run used
12345, clicking Random showed a new seed, and the next run used it.