I think he means that with the next rulebook such things must be clarified much like how with the 2011 rulebook all instances of stuff like "characters that have X" was changed to "characters that can use/possess". So that when the rulebook talks about movement it's actually about "movement" (the game term) and not about moving (real world term) the characters.

Here you're:
http://www.hcrealms.com/forum/showthread.php?t=287066

Read those orange posts and you'll see what I tried to explain.

So , there is no official ruling about KB + Multibased characters. And couldn't it be better to write it so we let all this mess aside?

I think it isn't so difficult to state a general rule, for example "KB path on a multibased character dependes on the square you're attacking at. Starting with that square you trace the KB path as usual. Neither of the base squares can move more squares than the others." Or something like that.

That thread is from 2010, and the rules have changed since it was made.
It's also worth noting that vlad was not a Deputy at that time, so you should ignore his orange.

I'm not sure what 'as usual' would mean in this case since, as you point out, there are no rules that cover this issue.
Personally, I have no problem letting the presiding judge decide how to resolve the issue when it arises - it doesn't happen often, and as far as I can tell it doesn't have a lot of impact either. An official ruling would be nice, but not necessary as I see it.

So now that you're one of the official deputies please help me to solve this ¿can a KB path go upstairs in the case of being Knocked Back as explained before?

If we're letting the local judge resolve this issues, its open to interpretation, which I think is great!
You have a semi-goofy "comic book world" judge? He rules that Super-Jimmy Olsen CAN knock back a figure to go right up the stairs and maybe off the other side! HILARIOUS!

You have a serious gamer-type who wants everything rooted in reality? Doesn't seem to make too much sense to knock someone UP the stairs...

The part that is left up to the judge to decide is how knock back effects multi-based figures.

It does not matter the size of the dial they cannot go up stairs/ladders by knock back as it states they cannot.

Well, THATS no fun!

Just use Unus the UnRapeAble. He makes a close cobat attack using TK and places them on a roof, his special power then says to give them knock back of 3 squares.

He can literally throw people over buildings.

The local judge is always the final authority on how to resolve things. It's nothing new.

2011 Core Rulebook page 10
"A character’s knock back path can’t continue
beyond a square that blocks movement, elevated
terrain of a higher elevation or the edge of the
map"

I think this applies when there is no stairs in your KB path, so you take KB damage by smashing the character against elevated terrain.

What I try to explain is that stair squares let you move through them so they don't block movement. This is the why is state that knocking back upstairs is permitted. Perhaps it's a problem of wording or my interpretation of the rules but I find it ambiguous.

They may not block movement, but the top of the stairs is still elevated terrain of a higher elevation, so the knockback path would end at the foot of the stairs.

... and the figure would be dealt KB damage. Right?

Correct, sir.