This is normal behavior: if you have set Image Capture to open Photo Mechanic when a camera or card is connected, then Photo Mechanic will open if your iPhone is connected and has photos in its Camera Roll. This is what I would want to happen, since I would want the option of transferring those photos to my computer.
The problem with Photo Mechanic (PM 4.6, Mac OSX 10.5.6, MacBook Pro, 3GB RAM), is that Photo Mechanic does not see the iPhone in the Ingest window and can not import the photos from the iPhone.
If I set Image Capture preferences to open anything other than Photo Mechanic--Image Capture itself, or Aperture, iPhoto, or Nikon Transfer--the iPhone appears and its photos can be imported.
Why can't Photo Mechanic see the iPhone and import photos from it?