I can't speak for whether or not it's intended/expected behavior, but I'd wager that minQuantity having a call to Random in it is your issue - probably the title is re-evaluating the expression (including generating another random number) whenever you reference minQuantity, rather than calculating a single value for the contract.
You could test this by NOT specifying the title (the wiki says a requirement will typically get a default value) and seeing if there's still an issue. That may not resolve the problem in a satisfactory way, but it would at least narrow it down.
Edit: Well, actually that doesn't really test it, but it works around it. TESTING it would be perhaps by using @minQuantity more than once in the title, or using it in yet another field, and seeing if that makes it pick 3 distinct values.