Can't capture enemy ships?

[Shahed]

Now I'm playing my 2nd campaign, as UP. I always 1) Chain shot, 2) Ball shot 3) Board while pounding the sides & astern.
It always works for me. I've got every single ship I boarded 100%, including a few 2nd liners from the French.

The only problem is that a capture apparently doesn't count as a kill, so no exp. I tried an experimental battle myself, captured everything of value (1 2nd liner, 2 heavy frigates) and sunk the last 2. Then I tried with autoresolve and I got 4 kills (1 escaped) plus exp. I didn't get any xp with the captures so it seems captures don't count as kills.