Hair pulling by another rabbit

Question
I have two female rabbits, both the same age, one a european rabbit, the other a dwarf lionhead.  They are about 5mths old, and I've had then since they were 8 weeks.  The european has started pulling the hair out of the lionhead, and it's leaving her with red sore patches on her fur.  
They live outside in a two story hutch, and I get them out every day and put them in their run, which is 55" wide.  I have toys and hideouts for them in the run, and plenty of grass and clover to eat.  I've been cleaning the patches with salt water, and they are healing, but every time they are out together it happens again.
Can you tell me why this is suddenly happening, as they've always been fine together, and don't seem to like being apart.
Thanks

Answer
I have no idea what a European rabbit is, lol. Not a breed I have ever heard of. Rabbits are territorial animals, and should not be together. They were fine when they were younger because that was the litter-mate mentality, but now that they are older they should be separated.