Dwarfs may be able to knock each other, but they can't actually harm each other without tantrums or loyalty cascades. Really, your pretty lucky, in my first fort(in 40.24), i conscripted vast numbers of idlers into the military, idlers who were often chronically depressed or angry due to my habit of ordering them to dump the rotting corpses of sieges, my inability to make more clothes and a few forgotten beasts who managed to get past my defences and killed a large chunk of fortress. In its last few years my fortress was in a near constant state of tantrums, which is not so bad when its civilians but when a high-level military dwarf tantrums, he can cave-in peoples skulls with his bare hands. Worse still, in 40.24(I'm not sure if its since been fixed), there was a bug where a thrown object would escalate conflicts to lethal, which since i kept all my(very unstable) military dwarfs in very close proximity, would often result in some of my military dwarfs suddenly trying to murder each other, which would sometimes take months as they struggled in vain to land a blow though the opponents very high-quality armour.
Regarding bug-reporting, it doubt this is a bug, since if you are fighting in very close proximity, it makes sense you would trip a lot.