SegmentGroup Deserialization

Hi,
I have a little bit trouble with the deserialization of a SegmentGroup...

My Model looks like this (only the relevant parts):

```c#
public class Edifact_IC
{
public UNB_Segment UNB { get; set; }
public IC_Message Message { get; set; }
public UNZ_Segment UNZ { get; set; }
}

[EdiMessage]
public class IC_Message
{
......
public List Ref { get; set; }
.....
}

//------SegmentGroups-----
[EdiSegmentGroup("RFF", "DTM"),EdiCondition("...", "...", Path = "RFF/0/0")]
public class SG1_Reference
{
public RFF_Segment Ref { get; set; }
public List Date { get; set; }
}

//------Segments-----
......
[EdiSegment, EdiPath("RFF")]
public class RFF_Segment
{
[EdiValue("X(3)", Mandatory = true, Path = "RFF/0/0")]
public string Qualifier { get; set; }

[EdiValue("X(70)", Mandatory = false, Path = "RFF/0/1")]
public string Reference { get; set; }
.....
}

```

If I try to deserialize following (only EDIFACT Snipped for testing):
`
UNA:+.? '
UNB+UNOC:3+XXXXXXXXXX:500+XXXXXXXXX:500+XXXXXX:0610+XXXXXXXXX++VL'
UNH+XXXXXXX+XXXXX:X:XXX:XX:2.3c'
RFF+AGI:XXXXX'
DTM+293:20181001060000:204'
UNZ+1+XXXXXXXXXXXX'
`

the "RFF-Segment" property (Ref) in "SG1_Reference" is always Null. The DTM-Segment in the same SegmentGroup is correct...

If I change the SegmentGroup Class to:

```c#
//------SegmentGroups-----
[EdiSegmentGroup("RFF", "DTM"),EdiCondition("...", "...", Path = "RFF/0/0")]
public class SG1_Reference : RFF_Segment
{
//public RFF_Segment Ref { get; set; }
public List Date { get; set; }
}
```

the deserialization works good, but I have now (obviously) not a RFF_Segment property but the "Qualifier" and "Reference" properties.

How do I change the SG1_Reference class that I have a RFF_Segment and a DTM_Segment property?

Reproduce the issue using the supplied EDIFACT snippet and the SG1_Reference, RFF_Segment, and DTM_Segment definitions. Trace the deserialization handling for the segment group and compare the nested RFF_Segment property with the inheritance variant. Done means both the RFF_Segment property and the DTM_Segment list are populated.

Written by the indexing model from the issue text.