This appears to be Python 3 specific. On 2.7.4 (Win7):
>>> import sys
>>> sys.stdin='abd'
>>>

With fresh 3.4 repository debug build, prompt never appears, ^C, ^D are ignored. Must close with window's [X] button. With fresh 3.3, get repeated [62312 refs] lines. One could guess that they are generated but suppressed in 3.4.

There is a possibility that this is specific to debug builds; I cannot currently build or run one for 2.7. However, there is no problem with Idle running (on Windows) with 3.3/3.4 pythonw-d. (In other words, see same behavior as 2.7 above.)