UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/49.0.2623.108 Chrome/49.0.2623.108 Safari/537.36

Steps to reproduce the problem:
similar to https://bugs.chromium.org/p/chromium/issues/detail?id=526883

1. go to appear.in, join a room, try to share a screen while having multiple chrome tabs open
2. the chrome tabs shown in the preview are black.
3. select some chrome tab to share it
4. focus tab. It will show a picture.

What is the expected behavior?
chrome windows can be shared even if not focused

What went wrong?
chrome windows can only be shared when they are focused.

Did this work before? Yes 

Chrome version: 50.0.2661.102 (Official Build) m (32-bit)  Channel: n/a
OS Version: 
Flash Version: 

same behaviour on meet.tokbox.com.
Windows 10, 10586 and 14316