Whilst researching for my answer to this related question: Where are the cast and crew logos in Game of Thrones opening credits from? I came across something peculiar. In the Season 1 title sequence some of the characters have the wrong house sigils next to their names.
For example, Emilia Clarke and Iain Glen both have Lannister Lions and Sophie Turner has the Targaryen Dragon (though there are others too):
I've seen claims this is because the actors chose their own sigils but have yet to find a reliable source for this. Though this article claims these aren't the sigils they'd pick themselves so that seems to contradict that theory.
In the later seasons these sigils have been corrected.
Does anyone know why this was the case?