Custom Style for Channel

[SiFor]

I have multiple styles on a site that has child styles of one parent style, my child styles just have small changes from the parent like the logo and some colours, the issue I have is when a new topic is started the parent style is used for the new thread template and not the child style of the forum the user is currently viewing.

I have "Custom Style for this Channel" set to the style I want with "Override Users' Style Choice " set to yes which works fine until a new topic is created.

How do I stop this from happening? Is it because they are child styles?