I think that Scott's hit the chord on the head.
It sounds like what you're describing as riffs is what we refer to as Layers. As described, a Riff is made up of layers, so you can create your bass layer, your rhythm layer, your clarinet layer, and your duck call layer and then they will all play back together while your record your lead layer.
Also, be sure to pay attention to your measure count in the current riff or you'll be recording additional lead licks in a new layer. If you are still recording, a new layer will be created when the end of the current riff is reached and it loops (unless you turn on "Single Shot Record"). The only damage is that you waste a layer, but it can get confusing if you're jsut jamming with the record button armed

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Tim