Using CCK Date with Date Repeat on Calendar I have a content type named Event.  It has a field name Date, which uses the jQuery pop-up with Repeat options.  It uses the To and From date, both of which are required.  The time zone conversion uses the Site time zone.

On the Calendar view, I've modified it to use as the Argument, the Date field from the Event content type.  This is also added to the Fields, as it's required to match the Argument.  On Filters, I've got Node Type=Event and Published=Yes.

Now, I create an Event and set the Date field for 3/17/2011 03:00 pm to 3/17/2011 05:00pm.  I then put on the Repeat a repeat for Every Day until March 20, 2011, with no exceptions or anything else.

Immediately after submitting it, I see that the node display only has repeats for March 17, March 18, and March 19.  This is also reflected on the Calendar.  But, then when I open the node in edit mode, it says the Repeat Until is set to March 21 now.  If I save it now, March 20 shows up on the node display, but now the edit form shows March 22.

Any ideas what might be going on?  I've tried playing with the time zone settings, and no luck.  Any help would be appreciated!
Here is a very recent issue thread that seems to match your problem:

http://drupal.org/node/1014664

The issue is very recent and it looks like a working patch has been rolled into the newest version of the module, so a quick update of the Date module, (specifically the Date-Repeat submodule) should fix you up.