About SP Worlds

Hi.

I've just started a world this morning using the 1.9-Pre2. It runs beautifully better than 1.8, I'm loving it so far.

Now that I jumped to 1.9-Pre3 some hours ago, I see no differences at all, mainly because it just fixed some bugs.

The thing is.. after 1 or 2 hours of playing, I notice lag.. and no, I don't mean the low FPS type of lag.

I basically tried to kill a cow just now and saw it flying, literally stucked on the air in front of me.

I think i've read a lot of time ago, that Single Player Worlds are Multiplayer Worlds hosted on your PC itself, or something along those lines.

Is there a way to actually modify that, to get a True Single Player Offline World?

Mainly to see if that little but annoying lag could be gone by doing that.

TL;DR

Since SP worlds are MP worlds hosted on your own PC, is there a way to create a truly offline SP world?

Thank you so much in advance for reading and greetings from Uruguay :)