Slitherine

I had an army garrisoned and the province got attacked. The attacker beat the province militia and immediately attacked the garrison and lost.
The game now assumed that I had lost the province and that I had gained the province (both in the after turn notifier). So the 'just conquered' status was triggered.

I think this is not justified in this situation. IMHO you should only own the province if you occupy it at the end of the turn.
That would also allow to pass through a province without conquering it. Something I would really love to be able to do.

may be only sacked status is ok

Something to improve yes. Not sure it will make in the next patch though, as there are some major things planned...

Is this something that needs changing?

Given a turn is a year this could represent a region being attacked and the city conquered, with alll the associate pillage, rape and destruction, in the early part of a year and then it is liberated later in the year. In this instance then I suggest there would be an impact on food, commerce, infrastructure etc.

I wouldn't change the way it works today.

agree - I like it.

to me it models the chaos such as lost records, petty theft, score settling etc that would go on while a town was captured and then retaken. Slaves are going to go missing, taxes amazingly get lost, you have a small band of deserters running around, none of it of any long term importance but enough to disrupt things for a while.

I do agree to all of this if the region was held for one turn (that is: owned at the end of the turn).

In the case presented here the enemy attacked and defeated the militia in the country and then immediately attacked the city and lost.
Here I would agree to a one turn 'raided' event to model the destruction during the attack. But a 5 year 'just conquered' modifier is IMHO a bit excessive. Especially since you get the same bonus if you conquer a province that has been owned for hundreds of years.

You could make it handle in reverse. It takes 4 (5?) turns to get rid of the 'Just Conquered' penalty, and then 4 (5?) turns to get rid of 'Under Pacification'. If the province is then retaken by its previous owner, maybe have them face a penalty proportionate to how long it has been in enemy hands. So if it was 9 turns away from being fully controlled, have an appropriate, minor 1 year 'Restoring Order' penalty. If it was under control for almost the full 8-10 years, the player should face an equally uphill struggle rooting out the new regime and taking care of all the new 'loyalists' who have spent the last nine years getting used to it.