Generally, a properly configured RadToolTip stays in the screen (provided there is enough room in the screen at all). In case the original position does not provide enough room in the viewport it will automatically try the opposite so that it stays in view.
How does your tooltip's markup look like? Have you set the needed properties like Width and Height (and then ShowEvent, HideEvent, RelativeTo, Position)? What I can assume for now is happening is that they (or at least the dimensions) are missing and you are using its load-on-demand mechanism - the tooltip is shown with the HTML elements' default dimensions (basically 0 by 0px) and it assumes the correct position, then content comes from the server and its stretches the HTML, so the position is no longer correct. We cannot know how much content is going to come in, so we cannot predefine a size. Generally the best approach is to have some standard layout for your user control/content you load inside so you can set the proper dimensions in the markup. This is the case with most of the online demos as well.
In case this is not possible in your case please read further.
Autosizing is a feature of the RadWindow, not of the RadToolTip, the closest you can have to it is to leave the browser to resize the HTML by setting some Height
(e.g. 70px to accomodate the loading sign), no Width
to auto. Then in the OnClientResponseEnd event fore it to reposition:
tooltip = Telerik.Web.UI.RadToolTip.getCurrent();
//you can also try calling this with some timeout 100 to 0 ms should suffice
//you can also try adding the following
//var popup = tooltip.get_popupElement();
//popup.style.width = "";
//popup.style.height = "";
If this also does not work for you I can suggest a more complex function that will also try to calculate dimensions and set them, not only clear them.
the Telerik team
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