instantiating melodyne on a clip, then removing the region effect, it appears that rather than returning the audio as it was before activating the region effect, the destructively edited version created in prep for the region effect is there, so that audio before and after the area is now gone unless it had been copied to another track.

Hi. Which version of SONAR and Melodyne do you use? I have not seen this myself.
All the best.

can you expand on how you are "removing the region effect" ?

latest version of Sonar, Melodyne 4.  To remove a region effect, I right-click on the clip in question, and under "region fx" select "remove region fx".
 
I would assume the same problem happens with other region effects.  I will try to look into it today.