You're probably not imagining it. Some dogs are con artists that way (mine is).
I am no expert (and I've not started training mine for a proper heel yet, either, I need him to mature a bit first), but what we were told to do when teaching heel is to only treat/praise for X number of steps in proper position. Start with just getting the dog in a proper position at your side - lure if you need to. Then treat for one or two correct steps, then three, then four, and continue increasing. We're supposed to ignore all behaviour in a not-correct position. No correction, no treat, continue walking and wait for the dog to come back to proper position. We can make abrupt turns, speed changes, etc, as necessary to encourage the dog to find and stay remain in the heel position.