Forum main category link defaults to vBulletin default style
 

I have a custom style that I have created. The first time I log in, when I follow this path of actions, I end up with the vBulletin default style:
1. click on 'Main Forum'.
2. above the 'Post New Thread' tab, there is a 'link' list for 'Forum - Main Category - Main Forum'
3. when I click on the 'Main Category' link for the first time after logging in, it takes me there but the style switches to the vBulletin default style.
4. Once I have switched to my custom style on that template, it will remain set until I log off.

Within the ACP panel, my site is set to default to my custom style. What setting did I miss?

Thanks.