This is in the latest patch 1.01 RC7
There is an issue when firing medium artillery that uses shell ammo. The ammo usage is not being attributed correctly to the firing artillery.
A simple test can replicate.
1. Start Western Front campaign as France. I also turn off the AI
2. Add 20 corps and 9 corps in Nancy to French 2nd Army.
3. Remove munitions unit from French 2nd Army as it only complicates the results
4. French 2nd Army now contains three medium artillery, 23e under the army, 17e under 20 corps and 18e under 9 corps
5. March 2nd Army to Metz with offensive posture.
6. Battle will result
In my test I saw the following although this is not a one off and can be repeated with slight variations.
23e fired 8 times and had 2 shells left from 36
17e fired 8 times and had 36 shells left from 36
18e fired 11 times and had 16 shells left from 36
That is a total of 27 firings costing 54 shells. 54 is the correct total but it's not attributed correctly to the firing unit.