I think you are confusing the validation itself with the condition. The 'condition' is not specific to the greaterorlessthan validation, it's on (almost) all validation rules, and just allows you to enter some custom PHP code to determine if you actually want to enforce the validation or not.
Anyway, after reading this thread, and doing some testing, I've updated this validations code to ...
1) Actually work with joined data. As far as I can tell, it would never have worked right with joined / repeated data.
2) I've added three more options, so you now have <, >, <=, >= and =. Which should solve your issue, and not require the workaround troester suggested with the Condition.
Changes should be in github.
-- hugh