The correct format for the CSI (called/calling station ID) is explained in RFC3580: uppercase and hyphen separated.

This code snipped for FreeRADIUS will capitalise and format correctly:

rewrite_calling_station_id {
if (Calling-Station-Id =~/([0-9a-f]{2})[-:]?([0-9a-f]{2})[-:.]?([0-9a-f]{2})[-:]?([0-9a-f]{2})[-:.]?([0-9a-f]{2})[-:]?([0-9a-f]{2})/i) {
update request {
Calling-Station-Id := "%{toupper:%{1}-%{2}-%{3}-%{4}-%{5}-%{6}}"
}
} else {
noop
}
}

Thanks to Matt Richards from Bath University for writing and sharing this code.