Hi Tim,When you add elements to a symbol in a document, the collection is no longer a symbol: it is a symbol plus, for example, a line. Or, if you have grouped the elements, what you think is a symbol is actually a Group that contains a symbol and a line.
The best way to edit symbols and maintain intended symbol functionality is to drag a symbol into your document, e.g. from Offline Libraries, then drag it from the document into My Libraries, which creates a new symbol file, then doubleclick on the symbol under My Libraries. This allows you to edit the 'original' symbol file where you can do anything you want. When you drag the edited symbol back into your document it is a true symbol and will behave as such.
To create a new Block Schematic symbol it is recommeded that you use the Symbol Wizard in the Tools menu.
I hope this is helpful.