Was this ever fixed? We are switching to Bing Maps and have the same problem. OSM had no issues. We are using 2014.3.1202.
Our custom provider is on top of the bing map. When the user zooms we have to provide a new source for the custom provider. Doing this brings Bing to the front (or sends the custom one to the back, not sure which). If I hide the Bing layer, then I can see my data.