yum grouplist doesn't display all groups

I've noticed in Fedora that the yum grouplist command doesn't actually display all the groups:

# yum grouplist | grep Virt
# yum grouplist | grep Virt | wc -l
0

However you can still see a group with groupinfo:

# yum groupinfo Virtualization
Loaded plugins: langpacks, list-data, presto, refresh-packagekit
Group: Virtualization
 Group-Id: virtualization
 Description: These packages provide a virtualization environment.

Apparently there can be a "hidden" tag on groups, as reported in this Bugzilla entry:

Bug 986531 - unhide all groups from yum grouplist

You can see all the groups with the yum grouplist hidden command:

# yum grouplist | wc -l
39
# yum grouplist hidden | wc -l
126