Changes to property using Property Interceptors not persisted to database

Below is the interceptor code. It is fairly ordinary.

The method TranslatePrefixtoRegEx mangles the property PrefixList and generates a default RegEx from it (it returns it as a string). Which is what I want to happen if PrefixRegEx happens to be null or empty.

#region Property Interceptors
[AfterGet(EntityPropertyNames.PrefixRegEx)]
public void PrefixRegExAfterGet (PropertyInterceptorArgs<StateRegionSub, string> args)
{
    var prefixRegEx = args.Value;

    if (String.IsNullOrWhiteSpace(prefixRegEx))
    {
        if (prefixRegEx == null)
            prefixRegEx = "";

        if (!String.IsNullOrWhiteSpace(PrefixList))
        {
            args.Value = TranslatePrefixToRegEx(PrefixList);
        }
    }
}

[BeforeSet(EntityPropertyNames.PrefixRegEx)]
public void PrefixRegExBeforeSet(PropertyInterceptorArgs<StateRegionSub, string> args)
{
    var prefixRegEx = args.Value;

    if (String.IsNullOrWhiteSpace(prefixRegEx))
    {
        if (prefixRegEx == null)
        {
            prefixRegEx = "";
        }

        if (!String.IsNullOrWhiteSpace(PrefixList))
        {
            args.Value = TranslatePrefixToRegEx(PrefixList);
        }
    }
}
#endregion

Update: