How to automatically update a shared contact list group?

I've just installed Openfire and the Spark client.

I've created an active directory group called "SparkUsers". I've added the appropriate users to the group and enabled "contact list group sharing".

I have 2 questions:

1. Instead of adding each individual user, can i add groups into the "sparkUsers" group? Should the groups be Security Groups of Distribution Groups?

2. After the initial log on, when the client gets the contact list items, i've made a change by adding/removing users to the active directory group, but the change isnt shown on the client which shows the initial contact list. I've tried logging off and on again and even restart the client but no change, even after a few hours. Should it update? How can i resolve it?