ActiveTcl 8.5.13 has now been released and, per ActiveState's usual practice of making only the current release and its immediate predecessor publicly downloadable, the ActiveTcl 8.5.11.1 release is no longer available at the URL above, as Vance noted.  8.5.13 includes fixes for other problems including another critical problem introduced in 8.5.12.x (Issue15574).  So, until the Python 3.3.1, 3.2.4, and 2.7.4 releases are available (which will include the workarounds for this issue) and if you do not have access to 8.5.11.1, one option is to patch IDLE yourself.

To assist in this, I have uploaded a shell script which will attempt to patch the python.org 3.3.0, 3.2.3, and 2.7.3 versions of IDLE if they are installed.  While I've tried to make it reasonably foolproof, examine and use at your own risk.  Download the attached file from this issue, patch_idle_issue_15853.sh, and run it in a terminal session.  It uses sudo so, on most systems, administrator access will be required.

See http://www.python.org/download/mac/tcltk/ for more information.