I built a simple form with the listview control on it. I added your code and a line '? button'. The code and the output seemed to be OK. Do you have any other methods or classes that could be getting in the way? You should also check your .OCX and .DLL versions. I was using the following:

comctl32.ocx - 5.01.4319 - 7/19/97
comctl32.dll - 4.72.2106.4 - 11/18/97