Pressed, Released and Clicked should be fired in the same manner w/wo Use Mouse for Touch option. These three events are fired at the same time when enabling the option.
1) Create a new widget, Make it added to viewport at begin play
2) Add a button, Add print string node for Pressed, Clicked, Released.
3) Run PIE, Try to press the button, Hold it for 1 sec then release.
Expected=Result: Pressed message will be seen right after LMB click on the button, then Released then Clicked message will follow release of LMB.
4) Go to Project settings, Enable 'Use Mouse for Touch'
5) Run PIE, Just like step 3)
Expected= Same behavior from step 3)
Result= Pressed,Released,Clicked events are fired simultaneously.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-66823 in the post.