Section 8.2 (node: Creating timestamps) of the info manual contains the
following description:

`C-c .'
     Prompt for a date and insert a corresponding time stamp.  When the
     cursor is at a previously used time stamp, it is updated to NOW.
     When this command is used twice in succession, a time range is
     inserted.  

In my opinion, the second sentence does not correspond to the actual
operation. To see this, one can perform a test on a single-line org file,
for example:

* TODO <2008-08-28 Thu> test todo item

We encounter (at least) the following types of behavior:

(1) point is within the timestamp, mouse cursor is either inside or outside
    (if inside, do not click). In that case entering `C-c .' will result in
    a timestamp update query, and hitting RETURN will produce no change in
    the timestamp.
(2) point is outside the timestamp, mouse cursor inside. In that case the
    `C-c .' command and RETURN will result in an updated timestamp at the
    point position while the original timestamp remains unchanged.
(3) point is within the timestamp. If after `C-c .' and the timestamp query
    one clicks on a date in the calendar, then the original timestamp will
    be changed to the selected date.

On examining the first two cases one concludes that the origin of the problem
is quite simple: In Case (1) the default answer to the update query is the
ORIGINAL VALUE OF TIMESTAMP while in Case (2) it is NOW. In my opinion it
should be NOW in both cases. Case (3) does not require comment as the
corresponding behavior is expected.

Additionally, if the previously suggested change be accepted, I propose that
the above description in the info manual be changed to the following:
    
`C-c .'
     Prompt for a date and insert a corresponding time stamp.  When the
     point or mouse cursor is at a previously used time stamp, the prompt
     requests an updated value, and the latter is inserted at point
     (default is NOW). When this command is used twice in succession, a
     time range is inserted.  

Regards,
bostjanv