I closed #14996 as a duplicate of this. The OP there claimed that behavior changed between 3.2.1 and 3.2.3 and that she had same problem with 32 bit installation. It is hard to know the exact circumstances of the problem until we find its cause.

Looking further, I am sure this is a tk and/or Win7 problem.
tkinter.filedialog.asksaveasfile() calls SaveAs(**options).show()
SaveAs sets command = "tk_getSaveFile" and inherits _Dialog which inherits commondialog.Dialog. The show method of that calls
tk.call(self.command, *w._options(self.options)). Since the test call has no options, self.options is an empty dict and I presume the serialized form w._options() is also. So the call amounts to
tk.call("tk_getSaveFile"), which suspends python until the dialog returns.

That said, 3.3.0a4 was released a week ago with tcl/tk upgraded, in the Windows installer, from 8.5.9 to 8.5.11. So I retried the previous test and the problem is gone. Can someone else verify? If so, we can close this as fixed. (I believe that the same upgrade will appear in future 3.2 and 2.7 releases, but I am not sure.)