Error and inconcistency when deleting form element after reordering

Problem/Motivation

When you reorder form elements and delete one element, you get an error:

"The submitted value -XX in the Weight for XXX element is not allowed."

Also the order of the elements seems to be returned to its original state after the deletion, but after saving the form, the elements are once again in the reordered state.

See attached video for an example.

Steps to reproduce

1. Open a form with multiple elements.
2. Reorder the elements.
3. Delete one element -> you get the error.
4. See that the order of the elements is the original order.
5. Save the form -> the order is now the reorded one.

Proposed resolution

There should be no error when deleting an element after reorder. The order of the elements should be consistent between these steps.