This is an issue that will not arise with creating new RenderTarget2D objects if you set your Graphics Profile object to GraphicsProfile.HiDef;
However, it appears that if you have not set this object in your application, MonoGame's internals will default to GraphicsProfile.Reach;
Help with this resolution came from the following thread...
The difference between these two settings is that the HiDef attribute will provide your application with the maximum capabilities of your graphics environment while limiting the device selection your application would be able to run on; in this case probably most mobile devices.
The Reach attribute will provide just the opposite capabilities by enforcing a limited set of graphic capabilities so your application can run on many different device types.
This should have been a relatively easy issue to resolve. However, the documentation within the Game Development Community is relatively poor forcing people who are learning the various frameworks to ask the same questions over and over again, which are then answered by those who have learned the idiosyncrasies of this type of development through experience.
Maybe some of us developers should get together and discuss developing a set of good documentation for the MonoGame environment that would allow newer developers to more easily resolve such issues.
Anyone interested ???