@mediaquery ignores padding property

@mediaquery is working well with all the properties except padding, which is ignored .. Why is this happening and how can I solve it? Is it a bug or what? .. I put my syntax in case it is badly encoded and I have not noticed (help please!):

@media ( max-width : 500px ) {
  header div {
  padding : 0;
  text-align : center;
  border: 1px solid red;
  }
}

I've also tried this (but it does not work either):

@media only screen and ( max-width : 500px ) {
  header div {
    padding : 0;
    text-align : center;
    border: 1px solid red;
 }
}