Hello Krisztian,
I am afraid the widgets cannot use shared datasource when filtering is enabled. Basically, the selected items are related to the content of the datasource. If it is filtered not by the widget itself, it thinks that the source is updated and the selected items will be updated accordingly.
What I would suggest you is to use a separate source for the widget. Thus the filter state will be preserved too.
Regards,
Georgi Krustev
Telerik
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