tcurdt/jdeb — comment on commit 68035698ea524a89bab88da5fc92b665a6db423b
File:  line 0
By ebourg:

Yes this is intended, even if the real encoding of the file is UTF-8 the round-trip with ISO-8859-1 will not corrupt the characters. The opposite would not be true, an invalid UTF-8 sequence would turn into the unknown character (U+FFFD) and then transformed back to ? in ISO-8859-1.