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If you´re using SfGrid with DataManager on adapter type WebAPI and you try to use advanced text filter options on nested property it generates a wrong filter query on final request.
On simple property this works during typing in dialog and press OK:

$filter=(startswith(tolower(Name),'a'))
On nested properties this will ALSO work during typing in dialog:
$filter=(startswith(tolower(Nested/Name),'a'))
But if you press OK than the DataManager generates a WRONG filter query:
$filter=(startswith(Parent/Name,null))
Same bug appears on each of this filter types: starts with/ends with/contains