interaction between --graph and --simplify-by-decoration

Hello,

  I've found that in some cases the --graph and
--simplify-by-decoration don't work well together. If you do this in
the git.git repository:

$ git log --graph --simplify-by-decoration --oneline v1.6.3.3
* cff4231 (tag: v1.6.3.3) GIT 1.6.3.3
* 6c7f58d (tag: v1.6.3.2) GIT 1.6.3.2
* 4774780 (tag: v1.6.3.1) GIT 1.6.3.1
* f01f109 (tag: v1.6.3) GIT 1.6.3
*   3536ae3 Sync with GIT 1.6.2.5
|\
| * a48f5d7 (tag: v1.6.2.5) GIT 1.6.2.5
| *   00f97c7 Merge branch 'maint-1.6.1' into maint
| |\
| | * bab39ed (tag: v1.6.1.4) GIT 1.6.1.4
* | | 503f464 (tag: v1.6.3-rc4) GIT 1.6.3-rc4
* | | 95110d7 (tag: v1.6.3-rc3) t4202: fix typo
* | | f29ac4f (tag: v1.6.3-rc2) GIT 1.6.3-rc2
 / /
| | *   66996ec Sync with 1.6.2.4
| | |\
| |_|/
|/| |
* | | 1f9b620 (tag: v1.6.2.4) GIT 1.6.2.4
| | * 77b96d6 (tag: v1.6.3-rc1) Update draft release notes to 1.6.3
| | * c965c02 (tag: v1.6.3-rc0) GIT 1.6.3-rc0
| |/
|/|

you can see that f29ac4f looks like it does not have any parents while
the correct parent is 66996ec which seems to have no children. But if
you omit the --oneline you can see that there are a lot of "root"-like
commits (f01f109, a48f5d7, f29ac4f,...).

gitk gets it right, and I've test also the first commit with both
flags and it happens the same.

Thanks,
Santi