Stopped production sites should produce something from their consumed wares befor they stop

I agree the building should continue doing whatever is in progress, but not start the next cycle if they are stopped. It should definitely not consume wares without giving anything in return. (Most likely the reason for stopping buildings is to conserve a particular ware and losing it without getting something it produces would be working against the intention.)

I've had some suspicions this might be happening, but never really sat down to investigate what happened to the buildings. If someone look into this, could they please check whether this is a regression from build18 (or earlier).

Definitively not a regression from build18 - this logic has not been touched, I am pretty confident about that.

I would say the trick is quite simple and no C++ coding is needed, just edit of conf files like below should be enough:

now:
[work]
sleep=43000
return=skipped unless economy needs blackwood
consume=log:2
animate=working 24000
produce=blackwood

changed:
[work]
sleep=43000
return=skipped unless economy needs blackwood
animate=working 24000
consume=log:2
produce=blackwood

What do you think? And as no serious coding is needed, anybody could do this.

This way, we would get working animations for buildings that aren't actually working due to lack of resources. So, it's not that simple.

good point. What about adding another step named f.e. check so the cycle would look like:

sleep=43000
return=skipped unless economy needs blackwood
check=log:2
animate=working 24000
consume=log:2
produce=blackwood

Worth considering... we would have to write a "check" program in C++ then. Also, we would have to make sure that all production programs have a check program in them, which is error prone. It might be easier to change the code in C++ to finish producing - we will have to look at the code though.

C code works the way that "work" can be interrupted after every step. So we would get two types of steps: ones that could allow interruption afterwards (perhaps the only one - sleep) and other ones that does not allow it.

I can prepare a fix (absolutely primitive) where stop would be effective only before first step in production cycle, otherwise the cycle will go on till the end even the building will me shown in state "stopped". What do you think?

Sounds good to me :)

Fixed in build19-rc1.