Came back home and indeed everything was still there, as promised.

Clarification question (to satisfy MaGog's curiosity): What triggers a sync from one's wishlist to your server?

I noticed that if I just changed a priority, it wasn't synced. But as soon as I reloaded the page or moved to another page, it was.

Probably another one:
1) Set a game to "High"
2) Made sure it was synced on the server
3) Changed the game to "Medium"
4) Reloaded the page (Ctrl-R)
5) The game reverted to "High" in the drop-down menu
6) Checked the server; it was correctly on "Medium"
7) Reloaded the page again; now it too was correctly on "Medium"

Opening a page (any page) or reloading. I toyed with doing it on every change, but that would mean a lot of AJAX at once, and possibly unpredictable results if they all hit the server at once (like some of them not actually being recorded properly) so I decided saving each change up and then just comparing a last edited and last updated date to see if new changes needed to be synced was best.

Most of the flaws in the system probably come from that, but it's the best I can come up with so far.
It's not quite a bug (as in I'm aware that that's what will happen), I just haven't figured out the best way to remove priorities from the list yet. For now I'm just leaving them, but I'll come up with something later.
That's definitely a bug. I can only imagine that the reload sending the new data to the server didn't finish before the data was requested (so the new stuff got uploaded properly but was missed) and then when you loaded again it worked correctly.
Is it a persistent problem or just a one off?

I can't seem to get any .js scripts to install in Pale Moon, both Adalia and Barefoot work and install fine in Firefox. Looks like Java is disabled without the choice to turn it on and I've tried installing the scripts before I installed NoScript too. Btw Greasemonkey installed fine in Pale Moon.

Any help is appreciated

I'm not sure I can be much help, there are some script bugs in Palemoon that I tried to fix a while back but I couldn't get Palemoon set up right for the script to work either...
There are a of [url=http://www.gog.com/forum/general/adalia_fundamentals_fixing_gog_so_you_dont_have_to/post557]users on Palemoon though, so it might be worth checking how they got things working.
I'm going to have to when I get back round to trying to fix the compatibility issues again..

Fair enough and thank you very much for your quick response. I'll ask and check around some more.

It's important to fix this because otherwise the database will grow over time, since obsolete entries (primarily games bought and removed from the wishlist) are kept indefinitely.

The solution is pretty simple, I believe. Assuming two data sets, one on the server, one arriving from the user:
- Update data set on server with changes from data set from user (you already do that)
- Then, for each id in (list of ids in data set on server),
if id is not in data set from user
delete id from data set on server

The one gotcha is the for each loop:
- If your language creates the full list of ids before beginning the loop, like perl does, you should have no problem
- If your language creates the list on fly, iterating over the data set itself (which you are potentially modifying by deleting from it), then you need to prepare a copy of the list before the loop and iterate on that copy, because you cannot safely iterate on a data set while deleting from it

This is persistent. Reproduces every time.

Yeah, but it's not urgent at the moment, and once implemented it will clean out all the obsolete entries anyway. I'll try and get something implemented for the next update.

That's not the problem, the problem is checking GoG side what games are no longer on the wishlist. I go through each page individually (when you view it) so the script never has a full image of the wishlist. I can't just remove any IDs not on the page your on because then it would only save one page at a time.

I'm fairly sure there is a GoG property somewhere in the userdata that lists all your wishlisted games (I'm sure I've seen one for all owned games, so there should be a wishlist one too) so my best bet is to find that, load it and then compare each entry against it to remove any redundant entries.

If that doesn't exist I'll have to think again about how to work it.

Thanks, I'll look into that then.

Here is the link:
https://www.gog.com/user/wishlist.json

Yep, that's the one. Thanks :)

Update:
Updated AF at work (sync is still disabled).
Opened wishlist at work.
Everything is again "not set".
Everything is again gone from server.

Did you open GoG at all before updating? Because the sync happens on any page.. so if you opened it first it would probably have cleared the server again before the update fixed the bug...
Which I forgot to consider / mention.
Sorry. It should work properly now though once you get home and it resyncs...
I might have a working backup of the server JSON now though so I'll see if I can restore it manually when I'm on my laptop and try again.

Yes. I did open GOG before updating. Sorry. Didn't think.
Will try again tomorrow.