write errors

[meine]

Hi,

I have a few files where I yank/paste some lines from the internet as a
reference. Often (not always) Vim gives some errors after `: wq`

E37: No write since last change
E162: nothing saved since last change of buffer "<path/filename>"
Type ENTER or type a command to continue

What is happening here, and how can I resolve it?

Further observations:

When this happens there are one or more files with the same filename,
but different 'file types', eg. with a .md file there is a .md~ and
sometimes an .mx .my. mz file, besides a .<filename>.md.swp which is
logical because editing the file wasn't formally closed in Vim.

Other observation is that there mostly is a strange character in the
markdown file, comming from the y/p from a browser. In many cases it is
a `¿`. When I replace that character and delete the temporary files, all
is right again.

TIA

//meine