UMLPackage sometimes does not let children go

[SuspiciousActivity]

Describe the bug

Children are sometimes not correctly removed from a parent element, the parent element just extends its bounds to include the child. This happens with ActivityDiagrams (if you move anything out of an Activity) and with UseCaseDiagrams (if you move a UseCase out of a System), but does not happen in a ClassDiagram (with a Package node) and in a DeploymentDiagram (with a Node).

To Reproduce

1. Open up Apollon
2. Create a new ActivityDiagram
3. Move an Activity node in there and make it big
4. Move an Action node into the Activity node
5. Move the Action node outside of the Activity node
6. The Activity node extends its bounds instead of letting the Action node go outside
7. Same goes for moving a UseCase node out of a System in a UseCaseDiagram

Expected behavior

The Action node should be able to move outside of the Activity node.

Screenshots

Before moving the Action outside:

After trying to move it outside:

Environment

 - OS: Windows 10
 - Browser: Chrome, Firefox
 - Version: Chrome 91.0.4472.124, Firefox 89.0.2

Additional context

I did some debugging on my own and it appears to me that when moving the Action outside, the Action in children here should not be there, at least this is the case in both working diagrams. While looking at the call stack, I also saw that in both working diagrams the call originates from here, while in the non-working diagrams, it does not.