This is indeed unfortunate. The main issue I think is that it was originally designed to have all singular names, but we fixed that but forgot the edmx internal names. These aren't available outside the EDMX, however are problematic with the wcf data service it seems as it leverages these names.
If you generate code using the Code First preset, you should be able to work around this, as you then don't get an edmx (it's regenerated by entity framework internally at app startup). Could you try that for me please?
If you want to keep using edmx (or have to, due to limitations in EF6's CF), you have to alter the template but the names of entities are in a lot of places so it's not that simple. We can't change it now as it's a breaking change. If CF works around it, I'd go that route.