Sorry to have been absent from this thread so long, tosca.
I have a house full of geriatric 32-bit machines. 
Unfortunately I didn’t have a 64-bit computer with me when I replied before.
I’m no expert, but I wasn’t suggesting switching to 32-bit. I use the 64-bit edition on my main writing computer, and I don’t notice any difference in 1.7.2.3, though I believe that with some older versions the 32-bit edition was sometimes better.
Indeed, in full screen mode the floating inspector window does not update to reflect the current sub-document but instead displays information for the sub-document selected before full screen was entered. This affects every section of Inspector, including synopsis (as you point out) and notes (which is a particular problem in academic writing). Personally I don’t edit in full screen scrivenings because of this and the text selection bug. For full-screen editing, I work with a single sub-document at a time, so inspector and mouse selection both work correctly. You can then use Alt+Shift+Up and Alt+Shift+Down to move between sub-documents in full screen, and inspector will update correctly.
Maybe someone will have a chance to fix this soon? 
This bug exists in Windows too and the Scrivener team is on it…