All the p tags with a br inside will collapse and not take up any space, the first line in the container will be "Some content" instead of that line being pushed down by the spacing p's. Testing in Prince 10r5p1 on El Capitan and CentOS.
Click refresh a few times. For some reason it's caching pages in a weird way. Another developer saw this listed and it took me refreshing the page 4-5 times before I saw the latest download/roadmap.
Hopefully this can be fixed soon as the the white-space rules are required to properly render tabs/spaces and currently it's completely broken. Tested in 10r6 on OSX El Capitan and CentOS.