On a serious note, I have noticed that (very recently) the popup windows that are generated when using the IMG, URL, etc buttons are taking a second to fill with their default text.
I'll try and take a screenshot of the empty ones, next time I see one. (They have a weird message) They do correct themselves pretty swiftly, so it's not a big issue at all. Just mentioning 'cos I never saw it before... and I use those IMG boxes a lot, but never seen it 'til recently.