Yes, I tried it on my Macbook Air and the same thing happened.
I just tried it with selectin 720p for the external monitor and it is stable and dislaying fine except the resolution is completely out.
I wonder if it will work better with a MDA to DVI cable - something in the LG manual says HDMI is for media sources not PC sources but I fail to see the difference - a signal is a signal isn't it?
The 'snow like effect' you describe could indicate you are experiencing timing/data corruption issues when sending a higher resolution data stream to the display. Could you post a picture showing the issue?
What type of HDMI cable are you using, and how long is it? If it's longer than 10 feet do you have a shorter 6 foot cable that you can test with to determine whether cable length is a factor? Not all cables are created equal.
What type of mini-DisplayPort to HDMI adapter are you using? Is it a good quality adapter?
Here's more info on MiniDisplay Port that may be helpful.
You gave me an idea and I tried another HDMI cable and it automatically just went to native 1080P and it seems fine.
Good thing I only paid $4 for it! Saves me $30 on a DVI adaptor I was going to buy.
I'm usually pretty logical with testing by exclusion but this time I assumed a cable is a cable.
Thanks for the inspiration,