From Matt Cutts' blog, 27 March 2006:
mattcutts.com/blog/q-a-thread- ...

Q: “I am seeing a lot of sites with “%09″ (tab) and “%20″ (space) in front of the URL in Googles index.”

A: I’ll ask someone about that.

So, it's not new.

It's probably because Google can't safely start assuming that you meant something different when you place a link.

since it reads and follows links found on other websites... there's no 100% reliable way to know if the webmaster made a mistake or not... so they take their word for it.