I've used XnView for quite some time, and decided to try out XnViewMP because its UI is a little bit more polished and straightforward, however, I'm having what I believe is a bug when previewing TGAs with the alpha channel enabled. Here is the same file open on both XnView and XnViewMP with the Alpha channel disabled:
Everything looks fine, but here's what happens when I enable the Alpha channel:
Lots of grid lines appear over the image. They disappear if the zoom is on 100%, but appear again as soon as I zoom in or out, which makes me believe it's an issue with how the zoom function works.