tooltip different from the first event to others

Hello to all,
I have a small problem, the graphical nature. That is when I create the first event, the tooltip is good and orderly, with gutter, when I go instead to create all other events, the tooltip that appears is borderless, and with a greyed out box just below the background text.

Here I would that all tooltips were equal to that of the first event.
If you need to see the problem, I can leave the link of the web page if needed.