Re;
Bug found. It seem that the reload feature is broken. See https://bugs.launchpad.net/ubuntu/+source/php5/+bug/1242376 for further details (two last comments are the most important here)
To resume, because the reload signal was not implemented in upstart < 1.10.0 the maintainer had the bad idea to comment out the reload line for the last PHP5 package source.
We cannot live with such a bug. Even if we can do a restart in place of a simple reload, this is not a way to go because on the panel as on many sites, the users will get an errors 500. Well, I'll fix this issue by comment out the upstart part which will allow to run the common init script in place.