Big news! I have both LAN and WiFi on all my Macs (WiFi for lication on maps etc). I turned off WiFi on both both Macs and now the other Macs find a LAN'ed world from one of the Macs!!!!
So - it's solved...though it's still a "bug" 'cause of course one should be able to have both LAN and WiFi on and that's no problem with MC 1.7 and MC 1.8.
So - when both LAN and WiFi connection of computers - at least Macs - the port scanning in MC is broken.
Direct connect works! But as LAN gives random number every time you LAN out a world it's not practical...my kids don't fix this to have to enter IP plus port number every time.
So - my theory is that MC 1.9 don't scan for LAN'ed MC's on local network...no scanning at all...maybe it scans IP but not port numbers? I don't know. What I know is that 1.7 and 1.8 always do the job. But not 1.9.
Crash report
So - I'm able to play MC over LAN with 1.8 - but not 1.9. And it's not a bug as you say...then I suppose it's a JAVA-thing. Ditect Connect gives "java.net.ConnectionExeption: Connection refused". I just wait for an JAVA update then.
Note: I can connect to MC-servers on Internet (some have updated now). So - my JAVA is OK for connecting over Internet - but not over LAN.
Yes - there is a firewall in settings on a Mac (came late in OSX development and many ask why) - no one use that - and as said - it's not on as default 'cause in Mac-universe no one cares about firewalls in OS (it's a Windows-thing).
Confirming: Direct Connect don't work. Gives:
java.net.ConnectionExeption: Connection refused.
I suppose you have Macs so you can see the real world yourself? Or is it only Win-machines in your lab?
I have no firewalls. We use only Mac's and firewalls is nothing I've used ever since I started with computers 30 years ago. 🙂 Maybe some Mac people should take care of this issue (Mac people normally have no firewalls - firewalls is a Windows-thing). So - LAN does not work WITHOUT firewalls.
If both Macs are ONLY on wired LAN = OK. If one or both Macs also have WiFi on = issue occurs.