From the provided information, it seems that all tooltip instances rendered on the client resolve to the same target element (e.g. the target element in the first instance of the rendered user control).
This will happen if your target control is rendered (multiple times) with the same client id on the client browser.
Please use the "View Source.." browser option to examine the ID of your [target control] image, as well as the TargetControlID setting of each tooltip.
The tooltips initialization strings are rendered at the bottom of the page and you can easily check whether they point to the same or different target controls.
the Telerik team