If you use socket.setdefaulttimeout() to set a socket 
timeout, and then do smtplib.starttls(), no data is read after 
TLS is started.

Here's a session that's as you'd expect:

>>> import smtplib
>>> s=smtplib.SMTP("smtp.example.com")
>>> s.set_debuglevel(1)
>>> s.helo()
send: 'helo mint-julep.mondoinfo.com\r\n'
reply: '250 smtpout-1.example.net\r\n'
reply: retcode (250); Msg: smtpout-1.example.net
(250, 'smtpout-1.example.net')
>>> s.starttls()
send: 'STARTTLS\r\n'
reply: '220 Ready to start TLS\r\n'
reply: retcode (220); Msg: Ready to start TLS
(220, 'Ready to start TLS')
>>> s.ehlo()
send: 'ehlo mint-julep.mondoinfo.com\r\n'
reply: '250-smtpout-1.example.net\r\n'
reply: '250-PIPELINING\r\n'
reply: '250-SIZE 32768000\r\n'
reply: '250-VRFY\r\n'
reply: '250-ETRN\r\n'
reply: '250-AUTH LOGIN PLAIN DIGEST-MD5\r\n'
reply: '250-AUTH=LOGIN PLAIN DIGEST-MD5\r\n'
reply: '250 8BITMIME\r\n'
reply: retcode (250); Msg: smtpout-1.example.net
PIPELINING
SIZE 32768000
VRFY
ETRN
AUTH LOGIN PLAIN DIGEST-MD5
AUTH=LOGIN PLAIN DIGEST-MD5
8BITMIME
(250,
 'smtpout-1.example.net\nPIPELINING\nSIZE 
32768000\nVRFY\nETRN\nAUTH LOGIN PLAIN DIGEST-
MD5\nAUTH=LOGIN PLAIN DIGEST-MD5\n8BITMIME')
>>> s.quit()
send: 'quit\r\n'
reply: '221 Bye\r\n'
reply: retcode (221); Msg: Bye

But if I set a socket timeout, I get this:

>>> import socket
>>> socket.setdefaulttimeout(30)
>>> s=smtplib.SMTP("smtp.example.com")
>>> s.set_debuglevel(1)
>>> s.helo()
send: 'helo mint-julep.mondoinfo.com\r\n'
reply: '250 smtpout-1.example.net\r\n'
reply: retcode (250); Msg: smtpout-1.example.net
(250, 'smtpout-1.example.net')
>>> s.starttls()
send: 'STARTTLS\r\n'
reply: '220 Ready to start TLS\r\n'
reply: retcode (220); Msg: Ready to start TLS
(220, 'Ready to start TLS')
>>> s.ehlo()
send: 'ehlo mint-julep.mondoinfo.com\r\n'
^CTraceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/Library/Frameworks/Python.framework/Versions/2.4/
lib/python2.4/smtplib.py", line 391, in ehlo
    (code,msg)=self.getreply()
  File "/Library/Frameworks/Python.framework/Versions/2.4/
lib/python2.4/smtplib.py", line 345, in getreply
    line = self.file.readline()
  File "/Library/Frameworks/Python.framework/Versions/2.4/
lib/python2.4/smtplib.py", line 160, in readline
    chr = self.sslobj.read(1)
KeyboardInterrupt

(I waited ten or fifteen seconds before typing the control-c.)

If I set the socket timeout back to None, it works correctly:

>>> socket.setdefaulttimeout(None)
>>> s=smtplib.SMTP("smtp.example.com")
>>> s.helo()
(250, 'smtpout-2.example.net')
>>> s.starttls()
(220, 'Ready to start TLS')
>>> s.ehlo()
(250,
 'smtpout-2.example.net\nPIPELINING\nSIZE 
32768000\nVRFY\nETRN\nAUTH LOGIN PLAIN DIGEST-
MD5\nAUTH=LOGIN PLAIN DIGEST-MD5\n8BITMIME')
>>> s.quit()

Logged In: YES 
user_id=849994

Fixed with the commit of patch #1380952.