Potential score corruption when using an Integer(method) pattern in score drl?

According to Mario this rule should normally work correctly (despite it being poorly written):

rule "qualification correct"
when
    $vehicle : Vehicle($vehicleQualifications:qualifications)
    $customer : Customer(vehicle==$vehicle,$customerQualification:qualifications)
    $test : Integer(RuleHelper.qualified($vehicleQualifications,$customerQualification)<1)
then
    scoreHolder.addHardConstraintMatch(kcontext, -100L);
end

But a user reports that it behaves as if it's causing score corruption:
https://stackoverflow.com/questions/51130220/rules-are-ignored-in-vehiclerouting-with-timewindows

Do a short investigation to see if you can reproduce this score corruption (and if not just close this issue). If you can reproduce it, it's a potential issue in drools.