Was posting about this on the discord, but there might be some kind of bug with collision events/qualifiers/flags
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Both objects in the frame have "Physics - Static" movement. Flag 0 is OFF for the green object and ON for the purple object - but the collision event seems to affect both even with a condition that checks the flag. (I can work around this by running a foreach loop on the object and testing in the loop instead)
If you change it to 'overlapping a backdrop' instead of 'collides with the background' it works.