Constraint : Transform extrapolation (bug ?)

Hello, Wise Blenderers.
2.53
I am trying to constraint gears with Transform Rot > Loc. I checked extrapolation but my Loc always comes back after a while. Is it a bug or am I a bug ?
The blend is to find at http://jpjb.eu/extra/Gears-trial.blend

Thanks in advance for checking what I do wrong.

See here: