This is a strange problem. After installing LEAP 15.1, my laptop starts booting when the lid is closed after a (completed) shutdown on AC power. Googling offers hints about malfunctioning sensors, but it seems this must be a software problem, given the perfect correlation - the problem started exactly after installing LEAP 15.1 and was not present in 42.3.
Any suggestions how to troubleshoot this problem will be much appreciated!