Automapper mapping issue concerning comma-delimited varchar field

Given the following:

SQL:

SuperClassTable
|
 --> NumberSet (varchar(MAX))
     Sample data: '110,111,112,113,114'

SubClassTable
|
 --> NumberSubSet (varchar(MAX))
     Sample data: '110,111,112'

SP_GetClassTables
|
 --> Returns the two tables above joined on an id, based on that id.

MODELS:

public class SuperClass {
    public IEnumerable<String> NumberSet { get; set; }
}

public class SubClass : SuperClass {
    public IEnumerable<String> NumberSubSet { get; set; }
}

MAPPER:

var superMapping = CreateMap<DbSuperClass, SuperClass>();
superMapping.ForMember(dest => dest.NumberSet,
                opt =>
                    opt.MapFrom(
                        src =>
                            !String.IsNullOrWhiteSpace(src.numberSet)
                                ? src.numberSet.Split(',')
                                    .Select(s => s.Trim())
                                    .ToEnumerable()
                                : null));

// Both of these map the comma-delimited varchars to 
//     the IEnumerable<String>s in the models.

var subMapping = CreateMap<DbSubClass, SubClass>();
subMapping.ForMember(dest => dest.NumberSubSet,
                opt =>
                    opt.MapFrom(
                        src =>
                            !String.IsNullOrWhiteSpace(src.numberSubSet)
                                ? src.numberSubSet.Split(',')
                                    .Select(s => s.Trim())
                                    .ToEnumerable()
                                : null));

CONTROLLER:

public class Repo{
    public SubClass Get(int id) {
        var subClassEntry =
            Context.Database.Query<DbSubClass>("SP_GetClassTables", new {value = id},
                commandType: CommandType.StoredProcedure).FirstOrDefault();
        var entry = Map(subClassEntry); // In-house method to take care of the mapping
        return entry;
    }
}

public class SubClassController {
    protected Repo _repo;
    // ...
    public ActionResult Edit(int id) {
        var model = _repo.Get(id);
        return View(model);
    }
}

VIEW:

@model SubClass
<p>
    NumberSet: @(Model.NumberSet == null || !Model.NumberSet.Any() ? 
                    "N/A" 
                    : ( Model.NumberSet.Count() > 1 
                        ? String.Join(",", Model.NumberSet) 
                        : Model.NumberSet.FirstOrDefault().Trim() )
                )
</p>
<p>
    NumberSubSet:  @(Model.NumberSubSet == null || !Model.NumberSubSet.Any() ? 
                        "N/A"
                        : ( Model.NumberSubSet.Count() > 1 
                            ? String.Join(",", Model.NumberSubSet) 
                            : Model.NumberSubSet.FirstOrDefault().Trim() )
                    )
</p>

PRODUCES:

NumberSet: 1,1,0,,,1,1,1,,,1,1,2,,,1,1,3,,,1,1,4

NumberSubSet: 110,111,112

I'm almost completely at a loss as to why it would do this. I tried removing the Splitting from the mapper and it created the same mess of commas. Any thoughts are most welcome.

(Note: this is from a much more complicated design that I tried my best to simplify for the sake of brevity, but I may have accidentally omitted an important detail or two in the process. My apologies in advance!)