Not much of a problem, some customers will knee-jerk refund for sure, but barring the game being a total mess (in which case it's not a flawed gem) most people will find something worthwhile to slug it out. Assuming the vendor actually takes steps to fix things so to not waste the goodwill of those customers.
Give customers some credit in that they will appreciate the situation on a developer by developer basis, that and if you release crap, don't cry about what follows.