This appears to be a new system wide problem with Sakai 11 (trunk). I cannot reproduce on Sakai 10-qa06.
Login as an regular user, iadd a tool with instructor/maintain (say Schedule), click permissions and remove the "Create Events" permission for all roles. Previously the permission changes were immediately reflected, apparent by the Add button no longer being available. (In some tools, the group permission may also needs to be removed)
Clicking Permissions and re-adding the permission should also reflect in the UI, making the button re-appear. "Create events" is just used as an easy to reproduce example.
On trunk there is no change to the UI and events can still be added, if you wait a few minutes or login as admin and reset caches it also updates.
This is mostly just keeping note of this as whatever is causing this problem likely would cause other problems (like possibly tool property changes not being applied immediately?) if merged back to 10 or when 11 is released.