WH2/3, Handgunners on guard sometimes keep on firing into melee trying to kill them..

I see this sometimes, not sure why it happens or how to force it to happen.

Usually, they just pull out their melee weapon and die or rout. But sometimes, they stand there "reloading" and unleash volley after volley against elite melee trying to kill them.

And they win. Because the entire ranks can shoot, while melee only fights in the first rank.

Is this a bug or something else?