Can't mention groups

Hi, According to this doc https://docs.gitlab.com/ce/user/group/#use-cases, I should be able to mention groups and subgroups in my project with the @group or @group/sub-group command, but it doesn't work: I can only mention the groups that I belong to.

Is this a bug ?

My gitlab CE install version is 12.0.3.

Details

Global groups setting

• My-organisation
  • department-1
  • department-2
  • dev-team
• external-dev-team

Project member setting:

Group	Permission
department-1	guest
department-2	guest
dev-team	developper
external-dev-team	developper

I belong to dev-team, and in issues and comment, I can only mention @dev-team : the auto-completer doesn't propose the other groups. But I can mention every single project's member in other groups…

Ty in advanced.