Help needed on log action with triggered rules

Hi,

I try to add an entry on a group stream when someone add a comment on a status.
To do that, I add a triggered rule and add an action to log the activity.

The rule is well triggered according to the debug trace :

0 ms "User saves a new comment on a status" has been invoked.
0.481 ms Executing the rule "New comment" on rule set "User saves a new comment on a status"
198.852 ms Action execution: "Show a configurable message on the site"
199.168 ms Evaluation of "User saves a new comment on a status" has been finished.

Options of the log activity action :
Visibility
Entities in whose stream activity records generated from this template should appear: *
Members of the active group
The users who will be able to see this message: *
The user in whose stream the activity will appear

But nothing happens in the group members stream.

Thanks for your help !