Ability to 'unshare' a post
Posts that have been shared by the user need an "unshare" option.
Dianara has this option implemented, but currently disabled due to the confusing effects of 'unsharing' an object. This is a Pump.io core issue. Unsharing a post doesn't really remove it from your Activity feed, or from other people's timelines, so it's not useful.
Until this is solved on the Pump core side, the "share" button on shared posts will show as "Unshare", but grayed out, disabled.