Steve,
Does your engine have two sets of middle rail rollers underneath of it? If so, then I would think that the engine won't stop until the last roller crosses the break in the center rail.
Or, it could be that your two center rails, even without a connecting pin, are just slightly touching.
Or, do you have a tender hooked to your engine, with a center rail roller underneath of it? (Like a whistle tender does?) If so, and the couplers between the tender and engine are metal, then the center rail power can still be flowing to your engine so long as the roller on the tender is still on the power side of the track.
Mannyrock
