There does seem to be something strange here. The figures that came out for [+pub_date+] are OK in as far as they are valid Unix timestamps, which Ditto needs for sorting, but they don’t match up to the dates you mentioned previously (they convert to Feb 25, Feb 2 and March 7 2010).
Another thing you can try in order to pinpoint the problem is Ditto’s debug mode. Add
&debug=`1` to your parameters, and you’ll get links to a table listing out what Ditto is receiving by way of data, what fields it is seeing and so on.

KP