I viewed both sonar and side scan tracks in the same window as in image RM2 Sonar 14.
When I swapped sides with the “Swap Sides” button, I get the result as in image RM2 Sonar 14 Sides Swapped.
I am not sure if this is by design, but I was expecting the Sonar view to rotate about the heading line but instead the port side stayed the same and the starboard side inverted but remained on the same side.

You're right - that shouldn't happen in the sonar viewer, and the behaviour you see in the map view is the correct behaviour. It is an issue with the way the file is cached in the sonar viewer - if you re-open the workspace (or restart RM) you should get the correct results in the sonar viewer as well. Will get it fixed.

Thanks Matt.
The workaround is easy enough.
However your answer made me realize that it is not only a visual swap in your current session, but a permanent swap recorded in the database similar to deleting track points.

It's a "permanent" change to the IDX file that we generate for storing sidescan and sonar image data (although not that "permanent" as you can always swap back!). It is intended to be used "once only" for a log, when that log has been recorded with the wrong settings in the unit (you can configure port/starboard on some devices). There is really no other reason to use this feature.