I can see how this could be confusing the first time it happens, but after that first time it should be clear that a new section has opened. I don’t like the idea of a button to go back to Research as notes can be opened from the Document and Fragments trees as well as Research, and from future sections down the road. The Research tree may not have been active at all during a particular writing session.
The Project toolbar buttons control the visible section on the right (Research, Notes, Daily Word Count and SmartEdit). Available sections are likely to grow over time — up from the current four. As well as the toolbar buttons, the F8 shortcut key will jump back to the Research tree (though there is a bug in there right now).
I’m guessing this is down to the Page Color button and dialog being removed a few versions ago. Without access to this button any background colors set for specific scenes cannot be changed. A workaround was implemented for just this case — where users had changed the color before the button was removed.
Go into your “Documents / Atomic Scribbler” folder (or “Documents / SmartEdit Writer”) and create a new text file called “color.txt” or just “color” if you can’t see file extensions. Re-open the current project and you should again see the Page Color button on the Word Processor toolbar.
You should remove any background color from your scenes, as this workaround won’t be maintained down the road. Background color is an underlying setting in the scene document, just as bold and italic are, so changes here are reflected in the actual end document. It was removed when the dark theme was introduced, as the plan is to use themes to set color in the user interface rather than document or font colors.