We have a strange situation and I'm at a loss how to investigate. If user1/securityRole1 gets a resolved case shared (read + share) with them, when they open the case it shows up as readonly (good) but the activity ribbon button is active. This means they can create a new activity regarding the resolved case (by clicking the button which auto populates the regarding field to the read only resolved case).
Meanwhile, the case owner/securityRole2 sees the button greyed out when viewing the case but can create a new activity by File/New/Activity and selecting the case as regarding manually.
User3/admin security role sees the same as the case owner.
If I add admin role to user1 the button gets greyed out and if I take admin role away again, it becomes enabled.
How can this be? Surely user1 cannot gain a right by having a role removed?
Any suggestions much appreciated.