duplicating levels can break entity limits

[pancelor]

Reproduction steps:

1. make a new project in LDTK 1.3.3
2. add a tile layer and an entity layer (I also added a tile layer but I suppose that's irrelevant)
3. configure the entity as "Max count 1 in the world, and move the last one when the max is reached"
4. zoom out to world view and duplicate the level. bug: both levels have a rainbow entity (you can't see the one in level0 in this screenshot, but it's still there). there are now 2 rainbows in the world, but the world was supposed to only ever have 1. (expected behavior: remove the rainbow in level0, I think?)
5. place more rainbow entities. bug: the second rainbow (from the new level) gets removed but the original rainbow stays

I removed the tile layer and uploaded the ldtk file here, in case it helps: https://gist.github.com/pancelor/eb44b3c20e97676504b597558a9ee3d0