Classification reference is created twice leading to invalid IFC

[Moult]

Here is my setting in Revit:

Here is the output in IFC - the reference is assigned twice. This only happens when the parameter is set to ClassificationCode, which probably leads to the double up.

This is what it looks like in IFC-SPF:

#18489= IFCRELASSOCIATESCLASSIFICATION('0MMhsys0H0weOeWTyE4N98',#42,'Uniclass 2015 Classification','',(#18466,#18466),#18488);

Notice the duplicate 18466.