While testing #15589, it appears that splitting custom editors and also resizing editors while being splitted can be challenging. Probably same cause as the docking panel split.

How to reproduce:

• Open a png file and a standard editor
• Try to have the 2 editors in parallel. Depending on which editor you land when trying to split, the mouse may not react. Same as resizing the splitted editors when the mouse goes on a custom editor.