I can’t get it to show up again on the current site I am working on as it must have been disabled from showing the tooltip again, but when I first toggled the Paste as text option in the WYSIWYG editor, I noticed that the tooltip warning that popped up was not fully visible at first and floated behind the editor window. If I recall correctly, it also seemed out of place.
Might be worth investigating if it is a simple z-index issue.
Cheers!