Error calling MS SQL Server stored procedure in VB.NET. A bug in VB.NET ?

I often call SQL Server stored procedures from VB.NET programs.

The error occurs for the following stored procedure:

     create procedure spDecimal(@in_arg decimal(10, 5),
                                                @out_arg decimal(10, 5) output)
     as
    begin
       set @out_arg = @in_arg
    end
    go

In fact, it does nothing more than giving back its first parameter.

The following VB.NET console application tries to call this stored procedure

'----------------------------------------------------------------------------------------------------
' Begin of code
Option Strict On
Option Explicit On
Imports System.Data.SqlClient

Module Module1
    Private sConnectionString As String = "Data Source=(local);initial         catalog=wrapper_test_db;User ID=sa;Password=sql;"

    Sub Main()
        Dim de1, de2 As Decimal
        de1 = 9.234D
        spDecimal(de1, de2)
        Console.WriteLine(de2)
    End Sub

    Public Sub spDecimal(ByVal in_arg As Decimal, _
                         ByRef out_arg As Decimal)
        Dim connection As SqlConnection = New SqlConnection(sConnectionString)
        Dim command As SqlCommand = New SqlCommand("spDecimal", connection)

        command.CommandType = CommandType.StoredProcedure
        command.Parameters.Add("@in_arg", SqlDbType.Decimal).Value = in_arg
        command.Parameters.Add("@out_arg", SqlDbType.Decimal).Value = out_arg
        command.Parameters("@out_arg").Direction = ParameterDirection.Output

        Try
            command.Connection.Open()
            command.ExecuteNonQuery()
        Finally
            command.Connection.Close()
        End Try

        out_arg = CType(command.Parameters("@out_arg").Value, Decimal)
    End Sub
End Module
'  End of code
'---------------------------------------------------------------------------------------------------------

Surprisingly, it prints 9 instead of expected value 9.234. The value of
output parameter is rounded.
This ONLY happens with the stored procedure with the parameter of type Decimal.
If we change the type of stored procedure to any other type (float, int, varchar etc.) and
change the type of corresponding parameters in VB.NET code, it works perfectly.

Does anybody have any idea about what happens with the decimal output parameter ?
Is there probably a bug in VB.NET ?

Gregory