Consider this, using python 3.4:
% python3
Python 3.4.2
% echo `python3 -c "print('a' * 72 + '\xff\xbe\xbf\xff')"` | hexdump -x
0000000 6161 6161 6161 6161 6161 6161 6161 6161
*
0000040 6161 6161 6161 6161 bfc3 bec2 bfc2 bfc3
0000050 000a
0000051
and this one, using python 2.7.9:
% python2 --version
Python 2.7.9
% echo `python2 -c "print('a' * 72 + '\xff\xbe\xbf\xff')"` | hexdump -x
0000000 6161 6161 6161 6161 6161 6161 6161 6161
*
0000040 6161 6161 6161 6161 beff ffbf 000a
000004d
Is this really a bug from python 3.4 implementation?