SqlDataReader in Debug and Release Configurations

Used in the project data retrieval using SqlDataReader'a:

IDataReader reader = cmd.ExecureReader();
DataTable table = new DataTable();
table.Load(reader);
reader.Close();


In the table from which data is taken, some columns do not allow storage of null . So, in the Debug configuration, all columns of the table table have AllowDBNull = true , and the Release configurations have full compliance with the table schema in the database — some columns have AllowDBNull = false .

Googling did nothing. Can someone tell me the explanation of this behavior, and tell you what other interesting things can hide SqlDataReader?