I found that the number of tweets was being included in the twitter request, before the filters to include retweets, hide replies etc etc
This meant that when I selected 'show 5 tweets', if 4 of the last 5 tweets were replies (hidden) only 1 tweet was shown.
To fix this, I added the following below line 613
if ( $args['items'] < 1 || 20 < $args['items'] ) $args['items'] = 10; /*thirz mod */ $showitems = $args['items']; $args['items'] = 20; /*end thirz */
and then changed the break at line 702 (after additions above) to
`/*thirz mod */
if ( ++$count >= $showitems)
obviously it's a bit approximate, because it still depends just how many (hidden) replies etc there are, but this worked for me, so thought I'd share in the hope you might do a better version :)