E-PL1: Camera autofocuses again after I try to use manual focus override

I am taking a photo of a very small object. I press 1/2 way to autofocus. However, I need to fine tune the focus. I press the magnifying glass button and use the focus ring (20mm f/1.7) to fine tune. When I try to take the photo, the camera autofocuses again, and overrides my manual focus setting. Can I preserve my manual focus, while still using AF for the prelim. focus? Or, do I need to turn off AF entirely?