I am afraid that the provided explanations are not enough to understand the problem. What I can assume is that you are using AJAX and you do not update and clear the tooltip when needed /e.g when the month is changed/. To test this assumption, please disable all the AJAX settings and test again. If this solves the problem, make sure that you clear the TargetControls collection and you update the manager every time you update the calendar.
A sample demo about AJAX scenario is available for the grid with paging (the logic behind this is the same as calendar with changing view - the core thing here is that the targets are updated):
If you need further assistance, please open a new support ticket and send me a simple, fully runnable demo along with detailed reproduction steps and explanations and I will do my best to help. After that you will be able to apply the same logic from the simple demo in your original application.
All the best,
the Telerik team
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