Is it common to end a Marie Curie IF fellowship early? Is it common for Marie Curie Individual Fellowships to end early? For example, if the scholar were to take up a permanent lecturing position after 1 year of a 2 year Marie Curie.

Would this be considered a bad thing to do? 

I'm curious if others have been in this position.
I don't know if it's common—one would require statistical evidence to answer that—but it certainly happens. A former colleague of mine finished a Marie Curie early (not a year, but perhaps 9 months) in order to take up a different position. In their case it was not even a permanent position, but another postdoc (a Veni grant in the Netherlands), although they obtained a permanent position not long after (and cut short their Veni to take it up).