it doesn't do any harm in practice

I don't know how you can say that after saying yourself that removing it also fixes the OP's problem.

Update: Well, you said that removing use open fixes the issue, but I doubt you're claiming that binmoding output handles leads to a decoding error, so that leaves the binmoding of the input handle.

In reply to Re^4: Confusing UTF-8 bug in CGI-script by ikegami
in thread Confusing UTF-8 bug in CGI-script by wanradt

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