> I’ve just found a bug.  On my machine, ‘guix package -p test -l 2d’
> and ‘guix package -p test -l’ should return the same set of
> generations, but the fourth generation is shown twice in the former
> case.

Generations 4 and 5 have the same creation date for some reason:

scheme@(guix ui)> dates-generations
$4 = ((1379357250 . 1) (1379364436 . 2) (1379364463 . 3) (1379364530 . 4) (1379364530 . 5) (1379419461 . 6))

Since this line

(map (cut assoc-ref dates-generations <>)

returns the first entry with the given key, the fourth generation is
printed twice.

I’ll try to replace the alist with something else.