[WYSIWYG] Pasting content with indentation into the editor flattens the indentation

If I copy and paste the following text:

into the editor, indentation is all flattened as follows:

• Item 1

• Item 2

• Item 2a

• Item 2b

• Item 3a

• Item 3b

I understand markdown is not supported, but I'd expect the indentation to be preserved in plain text.