Why do you want to go there with a party? And how is this a "bug"?
It's a bug because you used to be able to to enter preview with a party when the thing was on preview.
As for the potential uses of entering with a party, these are the ones I can think of off the top of my head:
Test stacking of stuff with friends, such as debuff or buffs. Test aggro capabilities with things that hit back in a controlled environment. Check healing capabilities, effects on stats, etc with a healer friend. Have a friend stand nearby for CA, but without your pet mucking up checking combat log procs.
There are probably more uses that can be thought of, but these are the ones I can think of off the top of my head.
Comments
And how is this a "bug"?
It used to work, it stopped working. As this was not mentioned in any patchnotes, I'm assuming it is a bug.
As for the potential uses of entering with a party, these are the ones I can think of off the top of my head:
Test stacking of stuff with friends, such as debuff or buffs.
Test aggro capabilities with things that hit back in a controlled environment.
Check healing capabilities, effects on stats, etc with a healer friend.
Have a friend stand nearby for CA, but without your pet mucking up checking combat log procs.
There are probably more uses that can be thought of, but these are the ones I can think of off the top of my head.