The issue will not be fixed since there is a big chance to introduce a breaking change. Nevertheless, there is a simple solution that could be use. The solution is to manually remove the hidden column from the ClientState on the client.
<script type="text/javascript">
function test() {
var gridID = $telerik.$(".RadGrid")[0].id;
var clientState = document.getElementById(gridID + "_ClientState");
var value = clientState.value;
if (value) {
var parsedValue = JSON.parse(value);
parsedValue.hidedColumns = [];
clientState.value = JSON.stringify(parsedValue);
}
}
</script>