Hi Heiko,
Thank you for logging this Bug Report. I can confirm this is indeed a bug and have added an issue in our public GitHub repository, where you can track the status of the item:
https://github.com/telerik/kendo-ui-core/issues/6146
Until the issue is fixed you can define the tools explicitly as suggested in the GitHub item.
Finally, as a token of gratitude for helping us identify this issue I have updated your Telerik points.
Regards,
Aleksandar
Progress Telerik
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