First of all, I use XnView 1.50 at Linux Slackware 9.0 with
fluxbox 0.1.14 window manager.
Everytime I open XnView (by running "xnview" without parameters), it shows a small window at top-left corner. No problem. Then, I choose "Browse". The window is opened at correct size (I maximized it in another run of XnView), which is 1020x719 (add some pixels of window border and some pixels for fluxbox "taskbar").

The problem is that the window is not positioned at top-left corner (coordinates 0x0), as I like. So, there is some unused space above window (I can see my background) and the "taskbar" is covered by XnView window.
Maybe you need to install fluxbox or WindowMaker to reproduce this. I didn't tried to open XnView within TWM (only for test purposes, of course).
There is another bug! I'm at browser window, so I double-click (or press enter) at a thumbnail to view that picture.

The view window is opened, but it is ALWAYS opened with top-left corner of window at center of screen. In other words, it is opened at position "490x280" (that isn't actually the center of screen). The problem is that ALWAYS I view a image, I need to move the window. I can't even click on "maximize" button, because it is off screen.
I hope you can reproduce these bugs.