About half?
Are you using a for loop looping through a brickgroup?
Use
while(isObject(%brick = brickgroup.getobject(0)))
%brick.delete();
To delete all bricks.
Can you see why?
echo(brickgroup.getobject(0));
"86575"
brickgroup.getobject(0).delete();
echo(brickgroup.getobject(0));
"83722"