Where does the wide character come from? You either need to tell perl that that output handle takes utf8 (with binmode or in the open), or if you want to treat that source of input as non-utf8, don't do whatever you are doing to make perl think it has utf8.

If you are using perl5.8.0 and have your locale set as utf8 (as is the default under some OS's), either changing to a non-utf8 locale or upgrading perl may help.

Note that use bytes is lexically scoped just like use warnings, and isn't a general panacea anyway; newer perls shouldn't encode things as utf8 unless they get lied to about the input.