Yep, but then again that doesn't explain the same circumstance when the SDF-1 is in 'cruiser' shape while earthbound (and both configurations, with the city onboard, are shown in the SDF series ). Unless, the city is on swivel plates as you mention - just seems to be the long way around...
Any other ideas? (Mods, sorry if this is too far off the Q&A charter of this thread)
This really isn't addressed too much in the series. My best guess would be it is caused by the artificial gravity on board. If the city did rotate, that would be a lot of rotating blocks to move. I doubt they had the time to reconfig an entire section of the ship just to rotate when in Strike mode.