I finally updated my main server to 4.7, and I'm seeing some very tenacious app side image caching in multiple apps.
Pre 4.7, once Iconic triggered a change to the image cache key, you would see the image start to regenerate in the apps almost immediately.
Now, the old images are hanging on for much longer, even though the new image has already been created and placed in the server side image cache.
The updated image might show up in the Library view within a few minutes (or not),