Workaround completed. Now B3 might be working properly. Here is output from bug #8893 reproduction.
It behaves just like Linux.
olidammara [~]$ uname -sr; python 8893.py
read : ['oink', 'oink']
readlines: ['oink\n', 'oink\n']
readline : http://bugs.python.org/file17542/fileobject.diff
is the patch I used.
That patch is for 2.6.5, where NetBSD's pkgsrc currently pulls 2.6.6.
There are only three hunks so I manually applied it and recompiled.
I wonder if anyone has experienced this same issue in other BSD variants.