Importer fails to detect jcr:mixinTypes being protected if package uses single-value property

When debugging a case where a package doesn't install on the headversion of vault I found out that if the property jcr:mixinTypes is defined as single valued property - the code properly detects and sets the mixin but subsequently fails on detecting this property being protected and therefore fails as it tries to set it in DocViewSaxImporter in the setUnprotectedProperties method.