In any window that uses TinyMCE, add some text into TinyMCE. Then shrink the window horizontally until you see the text disappear. Now return the window to full size and you will be unable to see that any text is in TinyMCE, nor will you be able to obtain a cursor nor add text in that area.

Now, if you attempt to submit the HTML, it will give you an error that you did not put anything into the TinyMCE editor (if it is required). If you click into TinyMCE, you will not see any cursor but if you enter text you will be able to submit the HTML as just the text that was in there prior to window resize.