Omo washing powder

I washed my boyfriends formal pants in our washing machine using Omo auto and it has literally stained his pants. I did not soak it or leave it for longer. Whilst ironing the pants i saw that the bottom was completely stained and the colour was no longer the same. It had the same effect that bleach would on a dark garment. This was not the first time but the second! You buy washing powder to clean your clothes not stain them!!!<br>