We just started seeing this same bug, and we're running 4.5 RC / 4.6 beta. In a nutshell, we were playing around with sending texture byte streams encoded as hex strings to Coherent, and we're debugging the messages being passed. The images aren't huge (say 1024x512 at most), but that's around 2M characters. If we log one and then open the console Unity totally freezes until you restart it. The console actually works fine if you're looking at another part of it; it only freezes once the particularly long message would need to be rendered.

This only seems to happen with very, very long strings. I know I've previously output JSON that we've sent to our backend in the console, with 10s to perhaps 100s of thousands of characters, and it works just fine.