Penn asked about the mortality increase. During the winter 1941-42 mortality went up among the Finnish population but the increase wasn't anything like among POW's. Especially young children and elderly died in greater numbers than in normal times. This is an indication that famine was already knocking on the door. I can check the exact numbers but we are not talking about full percentages as was the case with POW's but promilles. More like mortality increasing to 16 promille from 13, which meas about 10.000 extra deaths among the civilian population of about 3 million. On top of this came the military casualties.
In some closed hospitals, usually either for elderly or mentally ill, food situation became catastrophic and mortality rose. As far as I know this subject has not been researched in full but for example one hospital near Helsinki (Nikkilä) is known to have suffered in similar proportions as some POW camps. Hospital cook committed suicide because she could not do anyting about the situation.
None of the rations that could be delivered before new harvest 1942 were really what they were supposed to be on paper. Even if calories were there nutritious content was often very one sided an especially vitamins and fats were lacking. As Finland was very agrarian society those days most people could get at least a little extra from their own sources (hunting, fishing, own garden, own pig/rabbits etc.) and the wealthier in the cities resorted to black market. Relatives in the country side rose also to new value. In general, people managed through the period by using all available means and social connections. People without these, like those confined into hospitals, were in a very vulnerable position.
Rations provided for Finnish soldiers were not sufficient given the physical and mental strain they had to carry. Men often lost 5 to 10 kg of their weight. However, they were sufficient to keep the army going and far greater than those provided for other population groups.
POW's were initially given rations that corresponded those given to non working population. However, in many cases POW's had to work and often it was hard work. Given the disparity between the rations and work and taking into account that same problems that applied to rations in general also applied to POW rations, it was no wonder that the POW's got weaker, became sick and died in great numbers. POW's usually did not have any contacts outside of the camps and thus could not get any extra food anywhere.
If we look at the reasons why things went as they did, the most important was most likely that initially there was no centralised administration for POW's. Instead, Civil Guard was given the task and it had to organise very quickly a large number of camps for POW's. General Headquarters gave orders on food rations and certain other issues but did not have control or responsibility over POW's in general. This meant that a lot depended on the capabilities of the local Civil Guard personnel to organise things properly and what their attitude to the whole affair was. The new book that triggered off this discussion seems to indicate that there were extremely big differences between POW camps in this respect, but as I have not read the book yet I cannot say anything further.
The general headquarters took over administration of POW camps when the full extent of problems finally became clear and POWs started to die in great numbers February/March 1942. This coincided with a lull in the activity in the front, which perhaps explains why GHQ had not already previously intervened. In any case, the remedy was fairly quick and simple. Large number of POW's were sent to work to the country side as spring was approaching fast. This gave the prisoners the possibility to get more and better food. Official rations were also increased. It is noteworthy that even at the height of the catastrophe, based on explicit order of GHQ the International Red Cross was informed about the deaths. Help was also asked but given the war situation Red Cross could not do much.
What comes to attitudes, it is clear that many Finns hated Russians and that it showed in treatment of POW's.It is also clear that different groups of POW's were treated differently based on their "nationality" and that this was based on explicit orders. At the same time the expectation was that the war would be over by Christmas and thus POW's could be sent back to Russia. Nobody seems to have prepared for the long time solution that was eventually needed.
It is also clear that some rules and regulations applied to POW's were not in line with international law nor the agreements that Finland had signed. Especially the withdrawal of rations or diminishing them based on the behaviour of the POW were questionable methods to say the least given general lack of food.
So far at least no one has been able to find any evidence that the deaths of POWs' or civilians in the Russian Karelia under very similar circumstances, would have been the result of intentional policy. The ultimate reason seems to have been expectation of a short war, the failure of which brought Finland very close to famine because the government had not taken into account the supply problems that a long war brought with it. Later it was said that since the great famine of 1866-68, which was also partly caused by inability of the government to asses the situation correctly, Finnish population has never been as close to famine as in the winter 1941-42.