The red lock button will click visually into place (as shown) to obtain normal height by extending the leg slowly.

Note: I extended one of the legs too fast in my 1st field trial and the red lock button overshot its click position and I was soon holding a loose leg in my hand!

It's not a big deal to push it back till I hear that familiar click again. Always ensure that all the three red lock buttons are visible in their correct positions before using it.