As previously mentioned by Mike. All the text was bold, so bolding text was pointless.
I have set it so that text is forced as un-bolded unless otherwise stipulated.
By default, text in forums is not bold, but because of unclosed bold tags in some posts, it renders all consequent posts as bold.
This is why the first post or posts was not bold and then later everything was bold from a certain point.
By forcing it to be normal text, it overrides this problem.