I have already answered your question in the other support topic that you created about the same. I am posting it again here so that it is available to the community:
described weird behavior with the ScreenTip when you add a separator and
a footer is a known issue. We will address it in some of the next
releases. Unfortunately, I cannot find any suitable work-around for
this. Please, excuse us for the inconvenience.
All the best,
the Telerik team