it's a very corner case and don't have a good solution so far , probably need to document it.
please help prioritize this issue since its a corner case.
How rare this is really depends on the write pattern for the user table – it could potentially be a common scenario and not a corner case.
When Sean and I discussed a while back, we couldn’t think of an easy way to handle this. Haven’t thought through this very far, but it may potentially be easier to handle if we write an update as a delete and then an insert in the staging table?