When I do a quick left slide starting from the far right of the screen, it pulls up the Trash/Flag/More... menu bar and leaves it there.
If I do the same slide starting in the middle of the screen, it's sensitive to where it just goes to Trash and I don't get a chance to select the other options.
So I only start my left slide in the middle of the screen if I'm trying to trash it on purpose. If want to Flag it/etc, I start my left slide from the right side of the screen.