Thanks MightyPinecone, I suspected that much... but I wasn't sure if it mattered whether a file extension was lower or upper case (especially since Windows doesn't distinguish between the two when I try to rename the extension).
I'm going to try one of the methods recommended here and see if that works.

Edit: I managed to attach it – but I didn't even have to do anything this time. When I changed the Windows folder setting to show the file extension, it was correctly displayed as .jpg. And I haven't made any changes since I last tried to attach the damn thing. Strange...

That's odd because I've never had a problem attaching .JPG files to GOG forum posts before.

You also didn't have problems formatting tags within hyperlinks, including multiple links in the same row, and making new threads before, did you now?

And the tips on that site for how to change the file extensions should work. If you're running Windows 10 you can go into the 'View' tab in any folder and make sure the 'File name extensions' is checked (might be hidden if the folder is small, just maximize the folder and it should show up). If the files show their extensions you should be able to modify them simply by renaming them.
You might have stumbled upon a new forum feature. ;)

I have begun to empathize with the forum; it's past its prime and is slowly breaking down—just like me.

Edit:
Yeah, I can't explain that. Still, good to hear that you got it working!

Point taken! I'll stop using those adjectives in relation to any of the forum bugs. From now on I'll reserve 'odd', 'strange', 'weird' etc. for proper forum software behaviour. ;)

https://www.youtube.com/watch?v=AxK9qJCpH-8#t=0m32s

Aww, don't be so hard on yourself. At least you knew that lower case matters! ;)

I've just tried the same procedure with another .JPG file and found out exactly what happened in the former case...

Okay, so upon changing the extension to lower case .jpg and pressing the return key Windows (8.1) automatically changes it into .JPG. And, unsurprisingly, when I subsequently opt to hide filename extensions I'm still unable to attach said (.JPG) file. That goes without saying. However, if I then re-enable full filenames Windows suddenly recognizes the initial change into lower case and shows the file correctly as a .jpg!
I hope you get a good night's sleep MightyPinecone. :)

In Windows 10 (not sure about 8), if you change the capitalization in a filename and hit enter, it'll change it back, but you can just hit F5 to refresh and it'll show the new filename. This tells me that it's changing the filename when you hit enter, but it won't show up as having been changed until you refresh the window, navigate to another folder and then navigate back without using the back arrow or close and reopen File Explorer.

It works, thanks finkleroy! Silly, ignorant me, I had no idea you could hit F5 to refresh in File Explorer.

And on that rather embarrassing note, I'm going to bed.

Sorry that I wasn't clear. Glad you got it working though.

I vaguely remember one of those Microsoft vs. Unix debates as I recall Microsoft (and windows) not caring about the case of the extension while Unix sees it as a separate file name.

Neither in the extension nor anywhere else. The funny thing is that NTFS allows for case sensitiveness, it's the Windows file managing API that overrides the functionality.

That brings up an interesting question:

If you have two files on an NTFS drive that differ only in case, how does Windows react when you attempt to access one of them?

Also, apparently NTFS filenames are stored in Unicode; is Windows case sensitive to characters that exist in Unicode, but not ASCII?

By the way, try creating a file named "nul" (without the quotes, and with or without an extension) on Windows.

RE: the attaching of images and case sensitiveness, something has definitely changed in this forum's backend. I've just found out that the good old 'attach a text file disguised as an image' trick doesn't work anymore. So it seems as the forum now actually checks whether the uploaded file is actually an image or not.

I'd be curious about that too... or any other effects of saving a file which requires NTFS's POSIX personality (eg. using backslashes or colons in filenames), then looking at it through its Win32 personality.

(Like the NT kernel, NTFS was designed to allow modular frontends, so Windows NT could natively support Win32, OS/2, and UNIX apps simultaneously. On the kernel side, the OS/2 frontend is long dead, but WSL is the latest incarnation of their UNIX frontend.)

Heck, I'd be curious to see what the Linux ntfs-3g driver does if you feed it an NTFS filesystem containing null bytes in filenames, since apparently, NTFS uses Pascal-style strings (length+data) internally rather than C-style strings (data + null terminator) and the lower-level APIs allow paths containing null bytes.

To quote the post I linked:

For example, if you get the object manager into the mix (through redirecting via a mount point for example) only the following characters are illegal in the object manager:

[table here]

Quite a difference. Note that even NUL is valid as the NT kernel uses counted strings. The backslash is only invalid because without that there’d be no path separator. Obviously outside of NUL all these characters can be put into a Rooted Local Device path.

Not sure if this is something broken or if it's a change like the uploader but....

When I view my own wishlist with this url:

https://www.gog.com/account/wishlist

(Yes, I know that url is not the public one for folks to see.)

...previously the bundle discount was shown for Neverwinter Nights 2 was shown because I own the first one already.

When I click thru to the game:

https://www.gog.com/game/neverwinter_nights_2_complete

It takes a few seconds for the bundle discount to show up again.

When I go back to my wishlist url, the bundle pricing still isn;t shown.

It used to be though.