Thanks for your quick reply :-)
I had it set at "auto unicode", changed it to "auto unicode2", closed all open windows, exited the editor, renamed the original input file to some other name (to bypass the remembered encoding, if any), and the problem still persists.
Just to be sure a hotfix hadn't changed something, I downloaded the most recent hotfix as of today, applied it, and did the above procedure one more time (also renaming the file).
The problem persists. I am perplexed... I generally have the philosophy that I touch as few SlickEdit settings as possible, because it is a nightmare to get things right once they've gone wrong, so I don't think I've messed with some setting that breaks my installation. My setup is quite old, though, as I have a few custom languages and have exported and imported the same setup since SlickEdit 17 or so.
I just tried changing the encoding to UTF-8, in Options -> File Options -> Load. I guess I could live with forced UTF-8 encoding (without BOM) as this should be backwards compatible with my thousands of ASCII files. But, alas, this doesn't work either.
I don't think it is a Windows 10 issue as I had the same issue under Windows 8.1. Could it be a codepage issue? I live in Denmark so I my active code page is 850, according to the "chcp" command.
The only other thing I can think of is that I always open SlickEdit using a DOSKEY macro, never from the Start Menu. I don't know if this impacts some environment settings or SlickEdit's way of detecting the current code page, which again confuses SlickEdit somehow.
Is there some way I can reset all options, just to try it out? I only seem capable of finding a way of importing already saved options.
P.S. I just installed Notepad++ and tried with it and it works as expected: The BOM-less UTF-8 file is recognized as UTF-8.
Cheers,
Mikael