Why is `git blame` different from GitHub blame?

Question

If I clone bootstrap: git clone https://github.com/twbs/bootstrap

And then do a git blame: git blame js/src/alert.js

It looks like every line was last touched by the same guy:

^7ffb61a (Patrick H. Lauke 2017-04-17 00:04:49 +0100   1) import Util from './util'
^7ffb61a (Patrick H. Lauke 2017-04-17 00:04:49 +0100   2)
^7ffb61a (Patrick H. Lauke 2017-04-17 00:04:49 +0100   3)
^7ffb61a (Patrick H. Lauke 2017-04-17 00:04:49 +0100   4) /**
^7ffb61a (Patrick H. Lauke 2017-04-17 00:04:49 +0100   5)  * --------------------------------------------------------------------------
^7ffb61a (Patrick H. Lauke 2017-04-17 00:04:49 +0100   6)  * Bootstrap (v4.0.0-alpha.6): alert.js
^7ffb61a (Patrick H. Lauke 2017-04-17 00:04:49 +0100   7)  * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
...

But if I look at the blame view on GitHub I see a bunch of different people: https://github.com/twbs/bootstrap/blame/v4-dev/js/src/alert.js

What's with the discrepancy? Am I using git blame wrong?

Answer 1

If you do a clone with limited depth, and the last change happened prior to the earliest revision pulled, git blame will show incorrect results (I assume it's showing the person who did the earliest known commit).