Thanks for your immense patience about this matter. From now on, I am taking this case as a top priority and I will provide you almost instant replies so we can finish this project as quick as possible.
You can resolve this behavior by applying this configuration directly to the column:
columns.Bound(e => e.ProductName).Width(200).Filterable(f => f
.Operators(operators => operators
.ForString(str => str.Clear()
I've updated your Telerik points as a token of gratitute for bringing this issue to our attention. I will also forward this issue to our dev team for further investigation.