Ok, I see what it the problem.
It's because the system uses the first image of the listing in order to decide of the ideal size when you don't specify one of the dimensions for the thumbnails and since the normal image of your product is smaller that the dimension that you specified for the thumbnails, the system ignores it and it considers that no thumbnails are necessary for the images.
Please change the code:
if(empty($width)){
list($width, $height) = $this->scaleImage($theImage->width, $theImage->height, 0, $height);
}
if(empty($height)){
list($width, $height) = $this->scaleImage($theImage->width, $theImage->height, $width, 0);
}
to:
if(empty($width)){
if($theImage->height >= $height){
list($width, $height) = $this->scaleImage($theImage->width, $theImage->height, 0, $height);
}else{
$width=$this->image->main_thumbnail_x;
}
}
if(empty($height)){
if($theImage->width >= $width){
list($width, $height) = $this->scaleImage($theImage->width, $theImage->height, $width, 0);
}else{
$height=$this->image->main_thumbnail_y;
}
}
in the file administrator/components/com_hikashop/helpers/image.php and that should avoid that issue.