@zlefin
This seems to happen in 2.5 as well. The casualty selection is showing dragon x 3, dragon x 1 and dragon x 0. It does not matter how the 4 hits are divided, the system removes one dragon, sets one dragon as damaged, and 1 is unharmed.
I think that you are changing dragon, because I see the commented-out line about dragon_hit2.
Still, you are right this display of multi-hit units is very confusing and should be looked at.
Cheers...
P.S. After further checking, this does not happen in 2.5, as it takes 3 hits from non-hit units, and another from a 1 hit unit. As 2.6 will not take the 3 hits from the non-hit units. This will need a bug report with the regression label.
Cheers...