1.8.4 IDE will not use new sketches directory location

Development Tools IDE 1.x
1

I have 4 instances of Arduino installed.
2 on one laptop, and 2 on another.
On each laptop I have installed "arduino-1.6.13" and "arduino-1.8.4".

The reason for both "arduino-1.6.13" and "arduino-1.8.4" is all my sketches were in "arduino-1.6.13" and I had a reason to upgrade a while back though I cannot remember what that was now.

Perhaps I should just delete the old "arduino-1.6.13" instances as I have now copies of all the libraries and sketches in the new "arduino-1.8.4" instances.

In any case I moved the sketches location to my dropbox so I would always see the same stuff on each machine and not go to one machine and find I was on the wrong one for looking at a particular sketch.

To do this, in the Arduino IDE, I changed
File -> Sketchbook location to
/home/user/Dropbox/arduino_sketchbook_BACKUP_COPY_24.10.2017

This worked when I did it yesterday - Bingo! - I could open any of the 4 instances of the IDE and there were all my up to date dropbox sketches.

Tonight I tried again and all 4 instances of the Arduino IDE has retained
File -> Sketchbook location as
/home/user/Dropbox/arduino_sketchbook_BACKUP_COPY_24.10.2017

But It will not show the directory when I navigate to
File --> Sketchbook

Instead it shows my old sketches, and I have no idea if it backed these up somewhere; I deleted the old sketches directory.

What is happening and can I resolve this and use dropbox for my sketches?

(I remember in the past when I had this same problem with just one instance of the IDE; I can't remember if I solved it)

This rather clunky aspect of the Arduino IDE, I find, hampers creativity significantly.

2

Jasz:
all my sketches were in "arduino-1.6.13"

Don't ever put sketches or libraries in the Arduino IDE installation folder. Just leave that folder alone unless you have a very good reason.

Jasz:
Tonight I tried again and all 4 instances of the Arduino IDE has retained
File -> Sketchbook location as
/home/user/Dropbox/arduino_sketchbook_BACKUP_COPY_24.10.2017

But It will not show the directory when I navigate to
File --> Sketchbook

Instead it shows my old sketches

Sounds like a dropbox issue, not an Arduino IDE issue.

Jasz:
I have no idea if it backed these up somewhere; I deleted the old sketches directory.

It's easy enough to find out what's going on: Open one of the sketches in question, then do Sketch > Show sketch folder.

Jasz:
This rather clunky aspect of the Arduino IDE, I find, hampers creativity significantly.

What is this "clunky aspect" you refer to? You pick a sketchbook location and set that in preferences and then that's the sketchbook the IDE uses. What's clunky about that? It seems the only logical way to go about things to me. Of course you can store sketches anywhere you like. They just won't be accessible via the File > Sketchbook menu if they're not in the sketchbook but that's no big deal, you just have to open them via File > Open or by just opening the sketches directly.