Oddity In A MessageBox?

I have this

Dim st1 As String = sref.ConfirmLogin() 'A WCF method call.
Windows.Forms.MessageBox.Show(st1 & Environment.NewLine & "blue", "Result")

What is interesting about this is that there is no new line in the messagebox, and "blue" doesn't show up. If I reverse the order, then all is well. If I turn st1 into some other random string, all is well. However, as long as st1 is a string that comes from the WCF call, everything after st1 in the MessageBox is ignored.So what is coming from the WCF call?

The lines are these:

resp.GetResponseStream.Read(buff, 0, 99)
Return Encoding.ASCII.GetString(buff)

resp is a WebResponse object, though that shouldn't matter, as the key is that I take a stream, move it to a buffer, then turn that buffer into a string. What is it about the string that is alterning the way the string is displayed.If I highlight the "st1 & "Blue"" part, and press Shift+F9, it is all there. What I do notice is that there is a significant space beyond the end of st1 and before the Blue. Trim doesn't get rid of this space. My theory is that what is there is a series of Null bytes, and MessageBox is interpreting that as the end of the string and terminating the display at that point, even though it shouldn't really be terminated there. That's especially interesting because I can add in an Environment.NewLine, which would normally add a new line, but even that gets ignored.