bug in 'git describe'?

I think I've run in to a bug in 'git describe' (reproduced with git 
2.11.0, 2.16.1, and 2.19.0.221.g150f307af).

I've got two tiny git repos whose commit graphs are identical, but where 
'git describe' gives different results.

    *   merge 1.1 into 2.0  (HEAD -> release-2.0)
    |\
    | *   merge boo into 1.1  (tag: release/1.1.1, release-1.1)
    | |\
    | | * dummy commit  (boo)
    | * | dummy commit  (tag: release/1.1.0)
    * | |   merge feature into 2.0
    |\ \ \
    | * | | dummy commit  (feature)
    |/ / /
    * | | dummy commit  (tag: release/2.0.1)
    * | | dummy commit  (tag: release/2.0.0)
    |/ /
    * | dummy commit  (release-1.0)
    |/
    * dummy commit  (tag: release/1.0.0)

The tag 'release/1.0.0' is the first commit in history.

The histories differ only in the timestamps of the commits (and thus the 
SHAs of the commit objects).

Good repo: release/2.0.1-6-gbc33a04
Bad repo: release/2.0.1-8-g2c0a20c

Details, including full copies of both repos, here:

http://highlab.com/~seb/git-describe-bug/


-- 
Sebastian Kuzminsky