People are reporting numerous problems, ranging from some setting errors till false results.
Unfortunatelly, I am not planning to deal with COMSOL 4.0. Actually, I have tried once, and though new GUI should be better, it takes some time to adjust, that I didn't have.
So, I was thinking why to switch to someting else when finally I figured it out how COMSOL 3.5a works. And it took me a while to get there at first place. Thus, I cannot help with COMSOL 4.0.
Genneral things are transferrable, but the biggest problem in COMSOL 3.5 was where are important thing consealed in the GUI? That is the biggest problem with COMSOL manuals, if you ask me, since I cannot know how COMSOL programers are constructed GUI, and what did they put under "if constructions" behind each edit field.
I am sure that some changes are not related to GUI apperiance? Some things should be more simplified, meaning that if you want to set something manually in COMSOL 4.0, you need to dig very deep to find it, and it takes time.
All together, good luck with COMSOL 4.0.
ps. I guess browsing discussion for on COMSOL website might help