Reading a file bug in VB.NET? - vb.net

Question

The way this file works is there is a null buffer, then a user check sum then a byte that gives you the user name letter count, then a byte for how many bytes to skip to the next user and a byte for which user file the user keeps their settings in.
the loop with the usersm variable in the IF statement sets up the whole file stream for extraction. However with almost the exact same code the else clause specifically the str.Read(xnl, 0, usn - 1) in the else code appears to be reading the very beginning of the file despite the position of the filestream being set earlier, anyone know whats happening here?
this is in vb2005
Private Sub readusersdata(ByVal userdatafile As String)
ListView1.BeginUpdate()
ListView1.Items.Clear()
Using snxl As IO.Stream = IO.File.Open(userdatafile, IO.FileMode.Open)
Using str As New IO.StreamReader(snxl)
str.BaseStream.Position = 4
Dim usersm As Integer = str.BaseStream.ReadByte()
Dim users As Integer = usersm
While users > 0
If usersm = users Then
Dim trailtouser As Integer = 0
str.BaseStream.Position = 6
Dim ust As Integer = str.BaseStream.ReadByte()
str.BaseStream.Position = 8
Dim snb(ust - 1) As Char
str.ReadBlock(snb, 0, ust)
Dim bst = New String(snb)
If usersm = 1 Then
str.BaseStream.Position = 16
Else
str.BaseStream.Position = 15
End If
cLVN(ListView1, bst, str.BaseStream.ReadByte)
str.BaseStream.Position = 8 + snb.Length
str.BaseStream.Position += str.BaseStream.ReadByte + 1
Else
Dim usn As Integer = str.BaseStream.ReadByte
str.BaseStream.Position += 2
Dim chrpos As Integer = str.BaseStream.Position
Dim xnl(usn - 1) As Char
str.Read(xnl, 0, usn - 1)
Dim skpbyte As Integer = str.BaseStream.ReadByte
str.BaseStream.Position += 3
Dim udata As Integer = str.BaseStream.ReadByte
End If
users -= 1
End While
End Using
End Using
ListView1.EndUpdate()
End Sub

Answer 1

When you change the position of the underlying stream, the StreamReader doesn't know you've done that. If it's previously read "too much" data (deliberately, for the sake of efficiency - it tries to avoid doing lots of little reads on the underlying stream) then it will have buffered data that it'll use instead of talking directly to the repositioned stream. You need to call StreamReader.DiscardBufferedData after repositioning the stream to avoid that.