I have never seen anyone do this, when it rains folks put their brolly up and walk with it in the holder the entire time, plus of course it's a great place to keep towels and spare gloves dry hanging over the brolly spokesSorry. I've always thought the umbrella holder was for holding the umbrella while you're playing a shot and the trolley is stationary.
I wouldn't try and walk under the umbrella while it's attached to the trolley.
Not saying you've done anything wrong, I just can't see how it would be practical. But then I'm tall and it would be a struggle anyway.