Hi Antoine B,
Actually no need to call support on this issue.
You are correct that Symantec power eraser examine only load points of the current user & it's by design.
By default windows loads one profile at a time.
There are few common load point it can be specific to user profile.
Check following article to know more about it.
http://www.Symantec.com/docs/TECH99331
As per your comment -(the people doing the investigation in our company are not the same as the people that are infected, they do not use the same account etc.)- In this case people that are infected should run power eraser, investigation person should not use his login credential to run this tool.
However you can give request to product enhancement:
http://www.Symantec.com/business/support/index?page=content&id=TECH95412