The Class 333 electric trains used on the Airedale and Wharfedale lines are in many ways an excellent design.
The controls on the toilet door can sometimes cause problems if a member of the public is not paying attention.
The close button on the inside also locks the door. However its location means it can easily be pressed to close the door on exit (locking the door and preventing anyone else from using the toilet).
This does not happen very often, and the problem has been significantly reduced by putting a notice between the Open and Close buttons advising the public:
Please do not press the Close button when leaving the toilet.
The door will close automatically. Thank you.
An instruction is not really foolproof (as the fools get cleverer each day). Where possible we should design each product to avoid errors, what the Japanese call Poka Yoke or mistake proofing.