Ember server port permission

When doing ember s on any ember app, I get:

Serving on http://localhost:4200/
Livereload failed on http://localhost:49152.  It is either in use or you do not have permission.

Checking the failing port with lsof -iTCP:49152 shows nothing. So I guess this must be a permission issue. I installed this on a new Mac using the setup suggested at http://ift.tt/2ioObVn: brew install nvm, then nvm install 6.9.2, then npm install -g npm@latest.

I can start the server by using sudo ember s. But I can also start the server by explicitly assigning a different port for livereload – which doesn't make any sense given that nothing is blocking port 49152…

• nodejs 6.9.2
• nvm 0.32.1
• npm 3.10.9
• ember-cli 2.10.0

I'm confused as to what the exact cause of this problem is and how I can solve it. Any hints appreciated.