Why is the Tweet Button smaller than the others?

Hi there, great plugin but the Tweet button is smaller than the FB G+ and LinkedIn buttons.

Your screen shots show all 4 buttons should be the same so not sure why when I installed it, there aren't either.

I use ShareThis account which is linked to my Twitter account, so maybe linked users see the smaller default one, than users who don't have a twitter account linked to ShareThis?

Cheers.