Possible bug with private property read?

[Mark]

 Mock.NonPublic.Arrange<int>(mockedClass, "_prop").Returns(5);

Works as long as my private variable is setup like so:

private int _prop {get; set;}

However these:

private int _prop; 

or 

private int _prop = 5;

get an error attempting to read it. 

 

 

Thanks in advance, 

Mark 

 

[Mark]

Already know my own answer..
Backing fields aren't properties... sigh sleep helped