If you have a data validation, and there is an invalid field with the red border around it, if you hide this field via the filtering feature or the collapsing its group, the validation red border (and the tooltip) disappears.
To resolve this, you will need to update the ErrorTemplate of the input field (the TextBox). You can do this in the FieldLoaded event handler.
private void RadPropertyGrid_FieldLoaded(object sender, Telerik.Windows.Controls.Data.PropertyGrid.FieldEventArgs e){ if (e.Field.Content is TextBox) { var editor = (TextBox)e.Field.Content; var bindingExpression = BindingOperations.GetBindingExpression(editor, TextBox.TextProperty); if (bindingExpression.ValidationError != null) { var errorTemplate = Validation.GetErrorTemplate(editor); Validation.SetErrorTemplate(editor, null); Validation.SetErrorTemplate(editor, errorTemplate); } }