The HighlightItem objects that represent the UI of the special slots are rendered in a panel that is IsHitTestVisible=false, e.g. they do not receive mouse events and you cannot display a tooltip on them. This is because the slots' panel has to be on top of the appointments' panel and they should not interfere with each other.
Instead of using special slots you could use "special" appointments and handle them differently in the drag-drop behavior - for example, you could disable the drag and resize of the special appointments (this is easy) and when a "regular" appointment is dropped onto a "special" appointment, you could replace the "special", or do nothing, depending on your business logic. Or instead of replacement, you could hide the corresponding "special" appointment using the AppointmentsFilter functionality (let me know if you need an example about this feature, as the online demo example did not made it for the release).
the Telerik team
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