According to the provided information, it seems that you have enabled paging in your grid. I would like to note that RadGridView exposes two collections that contain data rows:
-Rows - contains all data rows that belong to RadGridView. Data operations such as grouping, sorting, filtering, etc. do not change the content of the collection or the order in which the row objects exist in the collection.
-ChildRows - returns the data rows that are currently represented by RadGridView in the order in which they appear. The collection is modified every time a data operation (grouping, sorting, filtering) occurs.
Similar to filtering, sorting, and grouping, the ChildRows collection is affected by the paging as well and it contains only the records on the current page. More information on this topic you can find here: https://docs.telerik.com/devtools/winforms/controls/gridview/rows/rows-vs-childrows
On the other hand the CheckFilteredRows property indicates whether the hidden rows should be checked by the header checkbox. If you have filtering operation, setting CheckFilteredRows to false it will not mark the hidden rows as checked when the applied filter is removed. And it will work fine in this case.
I tested the described scenario with both cases that you described on my end and I confirm there is an issue with the header checkbox. This is why I have logged it in our feedback portal by creating a public thread on your behalf. You can track its progress, subscribe for status changes, and add your comments on the following link - feedback item.
I have also updated your Telerik Points.
Following the information in the second post, it seems that you managed to found out a suitable workaround for this but then you have a problem when checking the header checkbox for the first time. In addition I can suggest setting the GridViewCheckBoxColumn.ShouldCheckDataRows to false. Please refer to the attached gif file to see the result on my end.
I have attached my test project as well. Could you please refer to it and see how it works?
I hope this helps. If you have other questions please let me know.
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