`write-region' writes different bytes than passed to it?

[Philipp Stephani <p.stephani2@gmail.com>]

Hi,

usually `write-region' uses the coding system bound to
`coding-system-for-write'. However, I've found a case where this
doesn't seem to be the case:

$ emacs -Q -batch -eval '(let ((coding-system-for-write (quote
utf-8-unix))) (write-region "\xC1\xB2" nil "/tmp/test.txt"))' && hd
/tmp/test.txt
00000000  f2                                                |.|
00000001

That is, instead of the byte sequence C1 B2 it writes the single byte
F2, which is an invalid UTF-8 sequence. Is that expected?

Thanks,
Philipp