Why is this property Getter virtual?

Having a strange issue with some C# code - the Getter method for a property is showing up as virtual when not explicitly marked.

The problem exhibits with the DbKey property on this class (code in full):

public class ProcessingContextKey : BusinessEntityKey, IProcessingContextKey
{
    public ProcessingContextKey()
    {
        // Nothing
    }

    public ProcessingContextKey(int dbKey)
    {
        this.mDbKey = dbKey;
    }

    public int DbKey
    {
        get { return this.mDbKey; }
        set { this.mDbKey = value; }
    }
    private int mDbKey;

    public override Type GetEntityType()
    {
        return typeof(IProcessingContextEntity);
    }
}

When I use reflection to inspect the DbKey property, I get the following (unexpected) result:

Type t = typeof(ProcessingContextKey);
PropertyInfo p = t.GetProperty("DbKey");
bool virtualGetter = p.GetGetMethod(true).IsVirtual; // True!
bool virtualSetter = p.GetSetMethod(true).IsVirtual; // False

Why does virtualGetter get set to True? I expected false, given that the property is neither abstract nor virtual.

For completeness - and for the remote possibilty they are relevant, here are the declarations for BusinessEntityKey, IProcessingContextKey, and IBusinessEntityKey:

public abstract class BusinessEntityKey : IBusinessEntityKey
{
    public abstract Type GetEntityType();
}

public interface IProcessingContextKey : IBusinessEntityKey 
{
    int DbKey { get; }
}

public interface IBusinessEntityKey
{
    Type GetEntityType();
}

Thanks in advance for your help.

Clarification - why does this matter to me?

We're using NHibernate and traced some issues with lazy loading to properties that were only half overridable - virtual getter but private setter. After fixing these up, we added a Unit test to catch any other places where thi