Is it possible, Myriam, that you had already given it a thumbs-up earlier? In that case, clicking it again would remove your earlier one and reduce the 4 to a 3 instead of increasing it to 5. After you clicked on it and posted the first time, the three people who had given it a thumbs-up did not include you. After that, someone else and you added a thumbs-up, bringing the number up to 5.
