Secondary Movement Strategy question

[BBegemott]

*TEST GAME

I have designed Destroyer with 1 Boarding Party V and 3 Explosive Warheads III. Primary movement strategy of Destroyer is set to 'Board Enemy Ships' and secondary on 'Kamikaze'. The idea is to capture non-shielded ships, if there are no available, then ram. I build 3 Destroyers and move them to guard the warp point.

Situation 1:
The enemy Escort1 with Phased Shields V & APB XIII warps in.
Result: 3 Destroyers are dead.

Situation 2:
The enemy Escort1 with Phased Shields V & APB XIII
and Escort2 with APB XIII & 2 PDC (no shields) warps in.
Result: Escort2 is taken, Escort1 is dead, one Destroyer is dead (2 Destroyers remaining).

This seems quite odd as in 2nd situation enemy had one extra ship and lost the battle.
In 1st situation all 3 destroyers attempt to capture Escort1, but as it has shields, they fail and become an easy target.
In 2nd situation Escort2 is captured; Escort1 shots and only then is rammed by the Destroyer, which captured Escort2 and has no Boarding Parties remaining.

It means Secondary movement strategy works out only if the primary weapons are not available(destroyed)? Isn't it a bug? It seems not logic at all.

P.S. Searched the FAQ, but couldn't find anything about secondary movement.