Most probably the described behavior comes form the applied changes in the ContentScrolling functionality. There was a logical problem in previous implementation but it is now fixed. When you have ContentScrolling = Auto you should explicitly provide sizes for the tooltip's width and height because the tooltip can't "understand" according to what size to create scrollbars or not. If you want to force the tooltip automatically calculate its size without generating scrollbars, you should set ContentScrolling = Default, which is a new enum value and the default setting of the property.
This being said, you should either set ContentScrolling = Default or set ContentScrolling = Auto along with explicit Width and Height values. I hope that my explanations are clear and helpful, let me know if you need further assistance.
All the best,
the Telerik team
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