I am not aware of a problem that may lead to the described result. That is why, I suppose that the problem is in your setup. In case you paste here the code of a simple test page that demonstrates this problem, I will do my best to help you find the cause for it.
In the meantime, you can try replacing the RadToolTipManager with a simple UpdatePanel - just load the content of the tooltip in the UpdatePanel. In case the page still reloads even though there is no RadToolTipManager on the page, then the problem is not in our control, but rather in your setup.
the Telerik team