i have just started running in my Capricorn engines, and i get the same thing. i didnt quite understand what you were trying to say, but now first hand i know.

when you raise the idle under rich conditions (run in) the slide actually start to lock up. the idle screw is stopping the slide form working freely. im sure once past the run in, when the engine is leaned off, the idle screw wont be screwed in as much. then it wont really be a problem. but something to be aware of.