When creating multiple nested taxonomies, duplicate parent terms are created

Problem/Motivation

The StrawSelection class contains a bug which creates duplicate terms when multiple new terms are created as child of a non-existent term.

I have created a taxonomy vocabulary and an entity reference field for the taxonomy which allows unlimited values and option 'Create referenced entities if they don't already exist' enabled.
Once I update or create a node and add two fields as child of a non-existent term, the non-existent term is created twice.

Example:
My taxonomy vocabulary list is empty. I add two terms to the node: "Test >> Test >> A" and "Test >> Test >> B". Once I save the node, the following terms are created:

Test
  |---- Test
             |---- A
Test
  |---- Test
             |---- B

The expected result is:

Test
  |---- Test
             |---- A
             |---- B