Hello,

After some further detailed research on the issue, it seems that it is not a bug, but an expected behavior due to the UI Virtualization. When the user filters, the rows are reused and the instance of the control defined in Column.CellTemplate is the same one. Thus, the styles gets mixed up as the instance of the control is reused.
You can check our online documentation on UI Virtualization for a further reference: http://www.telerik.com/help/wpf/radgridview-features-ui-virtualization.html.
In that case you can configure RadGridView with EnableRowVirtualizaton="False". Please note that this approach should be only used if you have a limited number of items displayed and no scrolling is really used.

Regards,
Didie