Unused Population

[Delta66]

Windows 7
V 2.22

After Capturing a enemy city I noticed that there were unused pop.
City population is 12, but only 7 pop are used!

Unused Pop.jpg (226.75 KiB) Viewed 677 times

By draging some of the 7 visible workers I can get all the 12 workers.

But I wonder if there is a way to send workers back to an unused pool.

I'm not sure if it a feature or a bug?

[Delta66]

Here is the saved game,
Check the city of Havel

[Delta66]

Afterward, I realized that this may be caused by my occupation of several production hexs in the city area, hence there were not enough room to field every workers, on the map.
However, it is strange that they were not send to work as scientists.