Depending upon where you click in a City Screen, it is possible to automatically reactivate the City Governor. For example, when you are in a City screen, if you single-click certain parts of the screen near where you assign citizens to individual squares, you will automatically reactivate the City Governor.
That behaviour could explain why you are seeing things being changed within the same turn.
Also, notice in the screenshot that r_rolo1 provided that a bunch of Specialists have been assigned by the currently-enabled City Governor. Why is that behaviour happening, you ask? It's because the City was recently captured from an enemy, and the City Governor will try and run as many Specialists as it can in that case. Could it be that you're talking about recently captured Cities?
If not, could it be that you have one of the Emphasize buttons enabled? I know that you said this fact wasn't the case, but the Emphasize Great People button will tend to hire a lot of Specialists.
See the image copy & pasted from r_rolo1's screenshot to see which buttons I am talking about:
Another possibility is that your City is somehow going to starve anyway, such as by having its squares Culturally stolen, by having a bunch of unhappy people from war or other factors, or by having a bunch of unhealthiness from an AI Poisoning the City's water supply or other factors. Basically, if the game thinks that you're going to lose a population point due to starvation ANYWAY, it might as well generate the maximum output for each of your citizens by intentionally running extra Specialists. However, you're likely only going to see a reassignment of your City's citizens within the same turn if the City Governor got reactivated.
Basically, if you can provide us with a screenshot or a saved game, it will be a lot easier to narrow down the specific problem that you are encountering. Look for the Attachments icon, as found in the following screenshot, and upload whatever you can get us (screenshots, saves, whatever). If you don't see that icon, click on the "Go Advanced" button and you should see it.