Indeed, it crashes in

TextIOWrapper_parseCookie(cookie=0xffbfb278, cookieObj=0x27e780)
_textio.c:1739
1739        cookie->start_pos     = * (Py_off_t *)(buffer + OFF_START_POS);

with a call stack of

#0  0x001426bc in TextIOWrapper_parseCookie (cookie=0xffbfb278,
    cookieObj=0x27e780) at _textio.c:1739
#1  0x001431f4 in TextIOWrapper_seek (self=0x545e38, args=0x70ce00)
    at _textio.c:1890
#2  0x001cef10 in PyCFunction_Call (func=0x715238, arg=0x70ce00, kw=0x0)
    at Objects/methodobject.c:81
...

The problem is that OFF_START_POS is 13, so the entire line produces an
unaligned access.