It sounds like the 1065 was prepared incorrectly. I see it all the time, but that doesn't make it right.
As a final K-1, there should have been income allocated to your client to bring the capital account to zero, but if you don't know what you're doing for the first part (allocated losses), you probably don't know that you're supposed to do the other (allocate income in final year). There are, of course, circumstances where that doesn't apply. Just depends...
I'm not sure I would feel comfortable playing tax rate arbitrage in the manner you're describing with this set of facts. However, I think there is an argument to say it's okay to do so.
~Captcook