It should not happen but if you are pulling it out very quickly it is possible. The same could apply after some years of using Walkstool due to the fact that the red plastic button can get soften after some year. In those cases there is no problem putting the lower leg back by pushing on both red buttons at the same time. It's the same procedure as when releasing the lower leg to wash it and then putting it back. This problem will not affect the security of sitting on Walkstool but always ensure that the red lock button is in the correct position and is visible after extending the telescopic legs to obtain normal seat height.