Hello bettati
I have been using that contrib for a long time now and have never had the whole group get my return message ... I am also in a group ... 3 groups to be exact.
We all use the Vacation contrib when ever we go on vacation or even when ppl leave the company .... it's a good way to let ppl know that a person is no longer here

Maybe you should contact Dungog ... there contact details are on the website.
Also check all your settings and see if maybe you have miss configured something.
Regards,
Tib