Hi,
it's a long time ago, that I have posted something about IM5, now I have more time to use it again, happily ...
So I'm not sure, if this little 'mistake' is allready nown or not:
I look at my pics in the Viewer and have switched on the Category Panel. Here I have selected the Current-window. If I leave the Viewer to select other pics and re-open the Viewer, then the Category Panel shows the Categories-Window and not the Current-Window, I have selected before.
This is the standard behavior.