The only "valid" thing I can see this arising from is when those lines of code were different, then converged to the same thing through subsequent edits. I've had this happen to me before, but none too frequently.
This is, of course, when it's time to factor out this common segment of code into new functionality.
That said, I can't think of any reasonable way to justify duplicate code. Look at why it's bad.
It's bad because a change in one place requires a change in multiple places. This is increased time, with a chance of bugs. By factoring it out, you maintain the code in a single, working location. After all, when you write a program you don't write it twice, why would a function be any different?
