I just ran into this problem on another platform.  I believe the problem is due to a sign-extension bug in the ncurses library unget_wch function (see link below).  It was apparently fixed in nurses 5.8; I've tested with the current ncurses 5.9 and test_ncurses now runs without error.

Are you using a version of libncurses/libncursew older than 5.8?  If so, can you try building with 5.8 or 5.9?

Another question is how to handle this for the 3.3.0 release.  It looks like not all platforms have the latest ncurses and, if not, the unget_wch function and test_curses are likely to fail.  Unfortunately, there doesn't seem to be an attribute available in the curses module that gives the version of the underlying curses/ncurses library.  At the least, the problem should probably be documented somewhere.

http://invisible-island.net/ncurses/NEWS.html#t20091010