Is this a Framemaker file that you are linking in Robohelp?
We do the following:
1. Create FrameMaker files for our content.
2. Create a project for RoboHelp.
3. Set up the properties of Webhelp (and point to a custom CSS file).
4. Publish Webhelp directly out of FrameMaker, pointing to the project file we created in step 2.
We created the custom CSS file by copying the CSS files that RoboHelp puts with every chapter when you publish to Webhelp. That was our starting point.
Those CSS files had a "caption" duplicate of all paragraph styles in it, so we just kept them.
The CSS file would be easier to maintain if we could simply delete all of the "caption" properties.
If you have you own custome CSS then you can avoid using caption properties,comment them out or even if you are deleting them make sure you copy them somewhere so if you need to apply them again in the doc somewhere,you dont need to create them again.