you will all be happy to know, that i have nailed the bug.

seems i like to be a starship trooper.

But the sad news is that it is in Bobboau´s fighter beam code.
if(test_collide.flags & MC_CHECK_SHIELD){ //if we're checking sheilds
int quad = get_quadrant(&test_collide.hit_point);//find wich quadrant we hit
if(Objects[shipp->objnum].shields[quad] < (bwi->damage * bwi->shield_factor * 2.0f)){
//then if the beam does more damage than that quadrant can take
//if(!(ship_is_shield_up(&Objects[shipp->objnum], get_quadrant(&test_collide.hit_point)))){
//go through the shield and hit the hull -Bobboau
if(widest > pair->b->radius * BEAM_AREA_PERCENT){
test_collide.radius = beam_get_widest(b) * 0.5f;
test_collide.flags = MC_CHECK_MODEL | MC_CHECK_SPHERELINE;
} else {
test_collide.flags = MC_CHECK_MODEL | MC_CHECK_RAY;
}
model_collide(&test_collide);
Objects[shipp->objnum].shields[quad]=0.0f; //for good measure-Bobboau
}
}
notice the last line
Objects[shipp->objnum].shields[quad]=0.0f; //for good measure-Bobboau
i commented this out, and the bug dissapeared.
right know i´m studing the fighter beam collision code, in order to determine if this accidently getting checked for shield-beam fighter collision when a cap ship fires a Big beam that collides with another ship.
or if it is a bug the code was born with.
will report back asap