The fact that browsers are buggy does not allow to list that as expected behavior. It's like "Some cars are made of paper and everyone dies in any collision >20km/h, but let's make this expected behavior" or "some chefs use cyanide instead of salt, therefore force salt manufacturers to add cyanide to all salt". These days it's not like deploying new version of browser to user requires major update to operating system, which would take 5 years to cover 90% of users.