The Image Picker works well for a “Create Post” use case but not well for an “Edit Post” type of use case because instead of defaulting to the post’s existing image, it defaults to whatever image it was used to pick last, which can be very confusing.
Anyway today I tried replacing the Image Picker with a Form with just an Image field. This works a lot better because you can both see the existing image and click on it to change it. I think I’m going to replace Image Pickers with one-field Forms everywhere. I thought I’d post this in case it helps anyone else with the same problem.