This has happened quite a few times now where I cancel my search and then the 'Mech launches into a match anyway. This last incident, I decided I wanted to swap in a bigger engine and change out a PPC for an ER PPC, so I cancelled my search. I then configured my Dragon Slayer and found that I needed to go pull the engine I wanted from another 'Mech. I saved the loadout and went to hunt for my engine. Lo and behold my DS had since launched into a match with
no engine.