Raw SQL result has it, result of ObjectContext.Translate<T> doesn't - sql

Question

I am able to replicate something I would have bet that is not true :-)
Entity-Framework-5 based application is populating an entity named "dbSetName" from stored procedure result, like this:
DbContext.Database.Initialize(false);
IDbCommand cmd = DbContext.Database.Connection.CreateCommand();
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = sprocName;
DbContext.Database.Connection.Open();
using (DbDataReader reader = (DbDataReader)cmd.ExecuteReader())
{
var tmpresult = ((IObjectContextAdapter)this.DbContext).ObjectContext.Translate<T>(reader, dbSetName, MergeOption.AppendOnly);
The reader is SqlDataReader. DbContext is derived from System.Data.Entity.DbContext - nothing fancy.
The stored procedure output, when I execute in SSMS, spits a single set - the result of the first and only stand-alone SELECT in its body. It consists of 3383 records.
The contents of tmpresult, when enumerated consists of 3383 records, but CONSISTENTLY and without apparent reason, a few records I see in the raw output are replaced with duplicates of records in the raw output.
For example, RAW output looks like this
Row Values
1.1 1.2 1.3
2.1 2.2 2.3
3.1 3.2 3.3
4.1 4.2 4.3
5.1 5.2 5.3
...
But the result in tmpresult is consistently like that:
Row Values
1.1 1.2 1.3
2.1 2.2 2.3
3.1 3.2 3.3
2.1 2.2 2.3
5.1 5.2 5.3
...
I can stop in the debugger, examine and ensure that I am executing the raw against same SQL server/database/sproc that EF uses... Bizarre...
Not sure what additional info to show, but I hope someone could explain this.
ADDITIONAL INFO: Replacing Objectcontext.translate<T> with SqlQuery<T> removes the issue. So do I now debug whatever assembly implements Objectcontext.translate<T>?