Hi matt,
When a paragraph tag is added via the Paste, it is just applied to the paragraph in the document as an override [along with the tag name], but FM doesn't add it into the document's internal catalog. You should notice an asterisk beside the paratag's name in the status bar indicating that this is a format that differs (or doesn't exist) from the catalog definition.
In order to add it to the Paragraph Catalog (so that you can apply it to other content or use this document as a template for other docs), you can either:
a) File > Utilities > Create and Apply Formats [however this will also take any override in the document and make a new catalog entry for these as well - you may get a rude shock from this operation].
b) place the cursor in the newly formatted paragraph and open the Paragraph Designer for the new tag. Then click on Update All at the bottom of the designer. This will update any paragraphs with this definition (i.e. only the one that you've just entered into the document) and add it to or update the Paragraph Catalog as required.
Option b is safer and more specific.