Comment 4 for bug 548981

dpkg does not touch this file itself; I imagine it's done by a trigger or something, although I don't know. However, dpkg itself does not provide a trigger that's run at the very end of an apt operation, because it does not know when that end would be. apt has Post-Invoke hooks, but if you use those then things won't work right if you run dpkg by hand.

It's not obvious to me what the correct solution is here. I don't think a change in dpkg is likely to be involved though ...