Valve's not sharing with us the full list of changes to the editor.
Heres a thread I started on the valve forum site about this topic. I posted my hammer and hl2.exe error logs there.
I have a map I have been developing that was almost ready to be released that about 10 minutes before the latest patch came out, ran perfectly fine. But ever since the patch has been released, it crashes with a HL2.exe error and I can not figure out what the problem is since I didnt change a darn thing. After working over 11 hours trying to fix this one issue, I have come to the conclusion that Valve is lying to the community on what changes they have made to the editor. I mean if it was only the four things they mention, I wouldn't have this problem in the least bit.
I have also noticed that a few custom maps also give me the HL2.exe error now after the patch including the balls maps you can find off this site.