A bounce will create a brand new wav in a brand new track, or tracks
A freeze will, in the case of a soft synth, create a new wav and place it in the audio portion of a Midi/Audio pair fo tracks. When you unfreeze - you go back to the Midi so naturally, the Audio is discarded.
Freezing a track should not delete the original waveform.
Make sure you know what you're freezing - tracks or synths