Users have the ability to add benefits to event registrations and have these values come out of the receipt amount for the event registration payment. Users can also change the host registrant to a different constituent, but find that after changing the constituent that the benefit isn't applied to the payment. For example if a user changes the host registrant from an organization, that isn't an actual individual that will show, to an actual individual record that will physically attend the event the benefits don't work correctly.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.