Hi Shaun!
Here are the general rules for how the Art Library behaves on the dev server. Is this not what you are experiencing?
Image Uploads on the Dev Server
When you search for art assets on the Dev Server using the Art Library tab, it will search through the images you have uploaded and tagged while on the Main server. You can use those images in your Dev Server games as well.
Drag-and-drop image uploads (when you just drag an image onto the tabletop to upload it) will be stored on the Dev Server. They will not show up in Art Library searches, they will not be listed in your Recent Uploads list after you close or reload your game, and they will not show up for use in Games on the Main Server. The advantage to be found here is that these images do not count towards your quota. Any image still in use in the game will still work if you copy it over from the Dev server to the main server.
It's best to use drag-and-drop uploads on Dev for quick one-off images (e.g. for testing or a map you'll only use once on Dev).