Apologies, Alex, I glanced at the screenshot and assumed the track had been frozen. John T nailed it when he said waveform preview is a "metering function". Purely a visual aid.
Freeze the synth, then drag the frozen clips into another audio track. At that point you can archive the synth, which you don't need anymore unless you want to edit the MIDI data behind it.
BTW, this is a technique I use often when I want to isolate and capture a single drum hit and apply special effects to it, like a big snare hit with reverb, or a reversed handclap. I've even transferred sounds from one synth to another this way, stealing a cool patch from a soft synth and loading it into, say, a Kontakt library.