To debug this issue, it would help to have the following information:
 - locale encoding: encoding variable
 - tested character: ch
 - character read by ncurses: read

Can someone reproducing the issue try to add: print("encoding=%s, ch=%r, read=%r" % (encoding, ch, read)) before the error?

It may be an issue in the Python implementation of unget_wch() or get_wch().

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> I believe the problem is due to a sign-extension bug in the ncurses library unget_wch function (see link below).

Can we workaround this issue in Python? For example, use value & 0xffffff?

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The test should be modified to use the encoding of stdscr, not the locale encoding: encoding = stdscr.encoding. (In this test, both encodings should be the same.)