Status ís Seen when user ís online, not really seen

[hantt12]

Steps:

1. There are more than 1 members in a channel
2. User A is opening the above channel in a browser tab, but currently not open that tab
3. User B send a message to the above channel
4. user B check who read the message

Expected result: User A is not in the list of who read the message

Actual result: List shows that user A read the message

[RomaricMourgues]

@rezk2ll this is about window being focused or not