1)The option to select indentation type (insert 
spaces or tabs) is missing
2) The indented width is ignored 

As a result IDLE 2.5 always indents inserting tabs, 
width 8

Sources edited in IDLE 2.4 cannot be corrected with 
IDLE 2.5:

The tabbing errors cannot be corrected with IDLE 2.5. 
You must revert to IDLE 2.4 

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user_id=149084

See IDLE NEWS for 1.2a1.

The ability to configure tab insertion as a default
didn't work, and was removed.  You can set the default
by changing config-main.def:  [Indent] use-spaces=0
but Python policy is to strongly encourage spaces 
instead of tabs.

For any edit window, you can switch to tab indentation
by using the Format / Toggle Tabs menu selection.  When
using Tabs in an edit window, the indent width must be
eight spaces because of Tk limitations.

If a file uses tabs, you have to toggle tabs 'on' before
you start editing it.  IDLE doesn't yet have the ability to
detect whether a file uses tabs or spaces.  (A TAB indicator
in the status line would be useful.)

Note that Tabs are always used in the Shell window.

I'm not sure what you mean by "cannot be corrected".
The Format menu has Tabify and Untabify.  I suspect it
might be clearer if the dialog asking for 'tab width'
was changed to ask for 'indent width'.  I am able to
change back and forth between tabs and spaces in any
region, but it does take some care.