It’s due to this:
$ git lg master v1.4.0.beta11
...
* | 9548876 - FIX: Some keyboard commands should not fire when anonymous (3 days ago) <Robin Ward>
* | 5b8917e - Version bump to v1.4.0.beta11 (3 days ago) <Neil Lalonde>
* | 4f890a4 - FIX: automatically load pages of topics list until it fills up the entire screen (3 days ago) <Régis Hanol>
| | * 53435cf - (tag: v1.4.0.beta11) Version bump to v1.4.0.beta11 (3 days ago) <Neil Lalonde>
| |/
|/|
* | 3ee5cea - fix the build (4 days ago) <Régis Hanol>
* | 31e8309 - FIX: ensure we never have a string when an enum is Fixnum - Take 2 (4 days ago) <Régis Hanol>
The beta tag isn’t included in the master branch, so git describe can’t use it…