I have a SharePoint 2010 (SP1 OCT 2012 CU) farm with two web applications. The root site collections of both these web applications have SharePoint groups that are showing no members in the UI. I can see the membership using Powershell to access them. I can add members with the UI, but cannot remove them. I can do everything with Powershell. Anybody have a similiar issue?
In Group Settings page of an SPGroup, there are two settings, "who can view membership" and "who can edit membership". You might need to set "who can view membership" to "everyone" and "who can edit membership" to "Group Members" or "Group Owner".
I think the account used to view group membership via UI is different than one used to access the group via powershell. And thats why you see a difference.