Hi, I am A. Stevens here to help with your question!
Could you please advise as to what platform your website is built on so that I can have a better idea of the editor?
Thanks for that information, also what browser are you using when you access your WP control panel to make these posts?
Could you try it again in chrome now to see if it might be a problem with the browser?
So there could be a number of things in Explorer. The easiest would be to restore the default settings for IE. If that does not work it may be something with some add-ons/extensions that might have been installed before.