Just a note that 3rd time was the charm here... after getting run-around by the first 2, Agent #3 put us back together without question.
However, the comment about upgrades is probably prophetic... That has happened to us as well, where I get upgraded and then whichever of us loses the coin-flip to stay in back ends up in a middle seat because we cannot change the non-1K passenger's seat outside of 24h w/o paying the fee.
Not a huge fan of DL in general, but I have to say that my overall annoyance level flying them lately has been microscopic compared to problem after problem after problem doing the simplest things on UA.