Using 11.15.2 beta 64bit
I have dual boot on currently on laptop/notebook to test and look into Win 8, but I have installed Win 7 to get some work done!
I have noticed that if the File Tree disappears under Win 7, I can R-Click the open area to the right of the files (or below if short list), and get a context menu that will show me a command "VIEW" to get the file tree back.
My original post here was going to say that I can't get that context menu to show up on the Win 8 system. But I just had a bright thought and chose to test one more way of interaction with the window.
In preferences - I made sure that the lines were showing and dark with color; and full row selection was activated.
I backed up the preferences for later use and tested the feature under Win 7.
Under Win 7, when I R-Clicked anywhere there was no WORDS, I got the context menu, which contained the VIEW command.
I went over to Win 8.1 and loaded OPUS and also RESTORED the preferences from Win 7 minutes earlier into this execution of OPUS under Win 8. I retested the same process.
The R-Click would only work if I very carefully put the point of the cursor on one of the lines that were there because of the choice to have Full Lines. But anywhere else, between the lines or below the name list would NOT work to show the context menu. And this is why I thought that the File Tree was not available under Win 8. This did not make any sense, so I am reporting the whole thing.
Also, I noticed that the Full Row Selection is not working either. Specifically in Win 8. But it may be a problem under Win 7 also.