Here’s a good one to confuse a sharing extension:
- Go into iBooks
- Open a book
- Tap the button to the book’s sort of menu screen
- Tap the Share button there
If you try to share using one of the system’s built-in services, such as Mail or Twitter, everything will go as expected. But attempting to use a third party one will have decidedly odd results.
For some reason, despite the activation rules each share extension has, the extension context from iBooks here has zero inputItems. At best, the extension will fail gracefully and cancel itself, or proceed on with no content. But there are plenty out there that get completely jammed — I presume an exception is thrown somewhere internal, and leaves the system stranded.