In article ,
says...

On 18 Sep 2018 21:52:37 GMT, Paul wrote:

I did a quick check here with the in-box "Paint",
selected just four files...

and they don't show up in a consistent order.

Thanks for confirming that the files don't show up in the desired order in
your tests, which, helpfully, knocks out a lot of variables (like is it
only Paint.NET - which it's not).

Even if I physically select the files, one by one, holding down the control
key, they _still_ show up in variable order.

The files in this particular case were nine screenshots, but my experience
over the years is that it doesn't matter what files I open as a group.

Long ago I tried to set the time stamps, and the file names, but in all
cases, the files shows up in a capricious order.

There _must_ be a reason for this.
Hence, there must be a simple solution.

But what?
First I tried disabling Windows Defender realtime protection,

That's a good test, but I'm not using any antivirus that I can remember.
I had malwarebytes but it expired a while ago.
(Maybe it's mad at me for not paying.)

If you want consistency, you might have to batch process
things.

I prefer to figure out, somehow, WHY the file order is capricious.
Once we know why, we can figure out how to solve it.

Unless the program has a macro recorder, and you're using a macro,
opening 400 windows one at a time, and mousing the image to death,
is nuts.

Actually, I misspoke about the 400 files as those are the *test* files.
They're all the same file which were created in batch by Irfanview.

I often edit a series of a dozen or more files since, like you Paul, I like
to prove that I always speak facts - where a screenshot is pretty good
proof of facts.

Too many times we get morons like nospam who just make everything up, where
they can never come up with a single screenshot of what they "say" they can

The same thing happens just copying/moving files or when using drag-n-
drop to drop a number of them on some program so they open. It's been
like that seems like forever and nothings ever been done about it.