Manual data creation: data jumps weirdly from a cell to another

Issue found

• When entering data manually by writing or copy pasting, occasionally a number or other content entered is duplicated and appears on rows below. At some point rows also become such that you can't delete them. 
• Snapshot: 186
• MacOS, M1

How to reproduce

1. Take the latest snapshot
2. Open Model editor from view menu
3. Create a model
4. Try to create a book model by writing or using copy/paste method from the example found in this page: https://wiki.qt.io/JSONListModel
5. You may see this:
   ManualDataCreationIsBuggy.mp4

How it is expected to work

• Entering manual data should be smooth, and the user should not see any extra information that has been written or copied in.
• It should be possible to delete rows of information, or empty cells.