I am attempting to load a cached Image Service into a basemap gallery. The image service does work, but it is behaving like a dynamic image service, not a cached one. By that, I mean that it is running a export image request each time the map pans instead of fetching the pregenerated tiles.
Here is a link to the service: https://gisservicemt.gov/arcgis/rest/services/MSL/Reference100k_cached/ImageServer
Here is the link to a jsFiddle demonstrating a basemap gallery with one tiled map service and one tiled image service.
If you watch the network traffic, you will see that the two basemaps handle the request very differently -- the tiled map service fetches map tiles, whereas the tile image service runs an exportImage task.
The service does behave like a cached service if I explicitly define it as a ArcGISTiledMapServiceLayer and load it to the map manually (without the use of the Basemap Gallery), so I believe this is an issue with the BasemapGallery itself.
I have a couple of ideas for work arounds, but thought I would check with the community before going down that road.