How to impex import classification values of type reference?

[lars_mueller3]

I do have the following scenario:

INSERT_UPDATE ClassificationAttribute;$classSystemVersion;code[unique=true]
;;singleOptions

;vehicleConfiguration;singleOptions;9;112;reference;true;;false;ZSmartECAT

INSERT_UPDATE ClassAttributeAssignment;$class;$attribute;position;$unit;attributeType(code[default=string]);multiValued[default=false];range[default=false];localized[default=true];referenceType(code)
;vehicleConfiguration;singleOptions;9;112;reference;true;;false;MyItemType

So far it works and the attribute shows up in the commerce backoffice.

Now I am trying to add data using impex

INSERT_UPDATE MyItemType;extraCode[unique=true];addonTitle[lang=$lang];&ref
;01;TEST 1;MyItemType_1
;02;TEST 2;MyItemType_2


$feature1=@singleOptions[$clAttrModifiers];
UPDATE Product;code[unique=true];$feature1(&ref);$catalogVersion;
;p0003;MyItemType_1, MyItemType_2;

Running the impex I get a null pointer for the &ref items.

any ideas about how to solve the problems?

P.S.: using the backoffice the assignment is not a problem at all

thanks!