[Bug c++/126869] [modules] Loss of character due to adding header

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126869

--- Comment #2 from d7d1cd <d7d1cd at mail dot ru> ---
(In reply to Patrick Palka from comment #1)
> Very related to PR124928 if not a dup

My actual case where I encountered this error isn't exactly the same as the one
I described above. While reducing the original code, I couldn't reproduce the
issue (but I did encounter a similar one described at the beginning of this
ticket). Now, I was able to reproduce the abbreviated example simply by
rearranging the lines for adding partitions in the module's interface.

Here's the abbreviated example: https://godbolt.org/z/PfjGT9eee . Apparently,
yes, it's a duplicate. And perhaps the bug in this ticket is also a duplicate.