Yes, ours moves too. We were surprised at first.
Unrelated, but we put a privacy shower curtain on a tension rod above the shower door. Dual function, if its outside the shower door and you have guests, it provides privacy if someone just HAS TO GO, while shower is in use. If it's flopped over the top and inside the shower door, you can leave the shower door open for more elbow room and the curtain keeps the water in, provides privacy too.
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