So, I discovered a bug in version 2.5- if screen data has the flag "First Enemy Carries Item" checked, and the first enemy is a bubble, they will carry the item, but when all other enemies on the screen are defeated, another copy of that item appears wherever it's placed in the room. So basically, the room is set up like this:
And this happens:
> 
> 
So the bubble drops the key, and one drops as if the flag "Enemies->Item" was checked.
Do you have the 'Enemies->Item' flag checked as well?
Nope, only "First Enemy Carries Item" is checked.
After some brief testing, I also discovered that the bubble only drops the item if the 'Hide Enemy Carried Items' Quest Rule if turned off. The bubble does not drop the item if that quest rule is on. But regardless of whether or not that rule is turned on, I did see a duplicate of the item being dropped where it was placed on the screen.
Confirmed.
Okay, this bug still happens in 2.50.1RC2.
Did you try to set the item but not place/set location on the screen?
I don't think it's possible to do that. You have to set a screen item before you can set its location. And even if you set the item location to the top-left corner, the item will still appear if you have one set.
Just hide the item in a bottom corner. Why would you want to give the bubble an item anyway? I couldn't get the damn thing to carry an item in the first place.
Well, that sort of worked. Because I just remembered that you can drag the item through the bottom and right ends of the screens. Thanks, SUCCESSOR.
Okay, I think I've finally got this working right. What it should do now is pick the first enemy in the list that doesn't have the "Doesn't Count As Beatable Enemy" flag checked.
Confirmed fixed.