As far as I can tell, this behavior is available in the form, but not available in grid edit. I would suggest submitting some feedback via Quickbase Uservoice. It is also possible that this is an unintended bug, so you might want to submit a support case. This isn't perfect user experience, but something you could do to make sure they didn't keep the value in reference field 2 after reference field 1 changes is use Custom data rules to ensure that whatever condition is applied in reference field 2 is also validated when saving grid edit.
