Just chiming in as a non-1911 guy. It sounds like your grip is affecting the gun in one way or other (engaging the safety or the safety grinding the slide with partial pressure).
I know on my plastic guns as the mag empties the recoil impulse changes and my grip has to adjust.
I don't know if it would be as dramatic with a steel (heavier) gun with only eight rounds as a plastic (lighter) gun with 20 rounds. But if you already know your grip may be a factor, that's were I'd start looking.
