Dynamic update of a running build's log adds extra empty lines in build output

When I open build's page, it correctly shows build output generated prior to the current moment. Then it starts to add more lines in the output because the build is still running (starting in the middle on the picture above), and these new lines are added with additional empty lines in between.

If I refresh the page, build output goes back to normal, but then again newly added lines are added with empty lines.

Looks like besides <br> dynamically added lines have \n symbols on their own (see web inspector on the right).

Chromium 51.0.2704.79 (64-bit)