henry0 - 1:45 pm on May 26, 2012 (gmt 0)
There are no precise answers as too many parameters are considered.
For example, the count is +1 for any tweet or retweet,
futher if a user tweets twice from the same URL it will count +2.
So you need to track more of the user behavior in order to figure out if anything is wrong.
Even more, due to the tweets volume Twitter might cache the button result and delaying the new sum, see where we go....