[Shotwell] Unconfirmed major photo loss bug running Shotwell under two Mint user accounts.

[Info Munky <info munky gmx com>]

Firstly, I'm not absolutely sure that the following is what has 
happened, but I think it is at this stage. Apologies if I'm barking up 
the wrong tree.

I had a large library of my photos in Shotwell under Linux Mint 18 on my 
laptop.
I also had some photos I was storing for other family members in another 
location.
As I like Shotwell so much, I thought wouldn't it be great to sort 
through the other peoples photos in Shotwell as I'm so used to it, but I 
don't want to mix them up with my own photos.
So I created a new Guest account in Mint, and put all the other peoples 
photos (henceforth referred to as Guest photos) in the Pictures folder 
under the Guest home folder. I ran Shotwell as the guest user, and sure 
enough had a separate Shotwell setup for the Guest photos.
However, I decided to change things around a bit, and re-import the 
Guest photos in a different folder structure, from scratch.

Here's what seems to have gone wrong:
I was logged into Mint as my main user account, I then switched user to 
the Guest account, and ran Shotwell, which showed, as expected the Guest 
photos. I selected all, and deleted to Shotwell Rubbish Bin. On exit, I 
selected 'Remove from library and trash files'. This gave me an empty 
Shotwell on the Guest account.
However later on I went back to my main user account and my Shotwell 
library has disappeared there too. Rather upsetting. I think my backup 
is up to date so I should be able to recover everything.

Possibly of note:
I did have a system crash when switching users back from Guest to Main, 
and had to do a hard reboot.

Can anybody shed any light on whether what I think has happened is possible?