subfolder mode

I must be doing something wrong, but I've paged through the manual a couple times so perhaps I'm overlooking this. 
When I open a directory in "Open in subfolder model" things initially work as expected. I see all the files from the top and subfolders in order in the filmstrip at the bottom of the FRV user interface (UI). 
But almost 90% of the time when I try to open 2-window mode and pick two images to show side by side, the UI completely resets and exits subfolder mode, showing only the files at the top level. Occasionally I can get it to stay open and compare two files. But no matter the order of the selection or dragging and dropping or any UI choices I make,  the UI almost always resets and exists subfolder mode.
I've tried paging through the forum(s) but I didn't immediately see a related thread. Nor did a google site: search find anything. 
If there is a specific order of operations for using 2-window in subfolder mode then let me know. Otherwise this feels like a UI bug!
Thank you! I love FWV and getting this working would be a huge benefit to me.