What if the divider lines of your ListView look like this? You wonder why when you clearly specified in your XML that the divider height should only be 1px. So why is it thick in alternating rows?
I am not saying this is the only solution but there is a big chance that this is the one. Check your AndroidManifest.xml and see if you have set a minimum and maximum version SDK required. If not, then add it. The divider height for your ListView will all be 1px.
Check the code below.
<uses-sdk android:maxSdkVersion="8" android:minSdkVersion="4" />
On a side note, this is also the solution for rating stars that are not displayed in crisp detail instead showing you blurred edges.