See attached image. This is the screen at the end of an attack by the Bulgarian I Army into a space in Romania. Bulgarians had six corps ready to go, but the battle ended after the first round with a Bulgarian retreat for no obvious reason. Even more interesting is the little box (circled in red) where the tooltip says "you have won a victory in this sub-battle". Likewise, the Romanian side has an indicator for having lost the sub-battle (also circled in red, near the top). The misplaced event tabs / message log are a result of the screen capture software I am using, so you can ignore that.
The bug here appears to be one that I've been noticing for a while: battles end (through a mandatory retreat) on a side that has lots of corps left to commit. The only way this can possibly happen is a "panic" morale check result. In this case, the Bulgarians attacked with a Veteran Corps (+1 morale check mod) and a NW mod of +1, so even on a 2 loss result, a "panic" morale result should not be possible. I've seen this same thing happen to the Germans attacking with +2 NW modifier and a veteran or elite corps.
So, a very basic element of combat is messed up (determining winners of battles / mandatory retreats), so this needs attention in the next patch.
Doug