Problem in case using multiple favicons in same domain

We have 'abc.com' and users have their own page with 'abc.com/userid'

Users set favicon for thier page, and published.

But some browsers(iOS Safari) replace all favicons in bookmarks which already exist

This is step:

1. I add bookmark 'abc.com/user1' with favicon 'user1.png'
2. I add bookmark 'abc.com/user2' with favicon 'user2.png'
3. Both bookmark image are same 'user2.png'

I can't find spec about it. I want to know whether favicon is unique for domain or not

Thanks