There is a problem when I use the custom filter, along with the default Telerik filters. When we try to filter on any Integer or decimal field, there is an internal JS error in the telerik grid. If we remove the custom filters then the filters work fine as it is.
demonstrates the usage of custom filters with no issues. If this is not the case at your end, however, you can open a formal support ticket, and send us the problematic code, in the form of a small working project. We will debug it locally, and advise you further.