I think I've inadvertently fired on friendly mechs before due to the "friendly" designation not appearing on the HUD, but I was able to document this a little better in this specific incident. I did a search on this and it seems like this has been an ongoing thing for a long time, which may be related to a line of sight issue. I didn't see any posts suggesting that it has to do with third person view, but that might be something to look out for.
In this image near the beginning of the game, you see a third-person-Nova with no friendly or enemy marking. You'll notice he has no triangle in the field nor on the map. I didn't shoot him because I knew there was no way an enemy Nova could be there that quickly (in the past I think I accidentally shot at a friendly Commando with no markings near the beginning of a match, thinking he was under ECM).
So decided to use the teammate status button (default "q"). I've read some posts that it may resolves the issue. But it did not in this case. As you can see, it works for the rest of the team, but our Nova friend still doesn't register.
This is a few seconds later. He still does not have any designation on the radar or field.
However, just a few seconds later, everything seems alright. Both on the radar and in plain sight with the teammate status button. I notice that he no longer has the third person view probe.
Obviously, one can see that this can be a problem. Someone mistakenly fires on a friendly that doesn't have any visual designation. The guy who got fired on then calls for his lancemates to retaliate, and then you have two or more dead mechs on your team (of course it's happened to me). I'm not sure if this is related to 3pv, but if a similar incident happens, look out for it and report your findings/file a ticket.
Edited by Takashi Uchida, 30 June 2014 - 07:47 PM.