If a file has quickshare enabled and you delete this file, the quickshare link becomes invalid too. Which is right.
If you then recover this file from the thrashbin, the quickshare link shows enabled, but is stlil invalid when you try to access this link.
Unsharing isn't possible anymore as well.
Both shouldn't happen.
Steps to reproduce
1. Upload a file in your Site
2. Make it Shareable by clicking on the Share link.
3. Check that you can access the public link successfully
4. Now delete the file.
5. Check that you can't access the public link anymore
6. Recover the file again from the bin.
7. Try to access the public link: you're shown that the page is unavailable and that the public link is removed.
8. Trying to fix this, in Share try to unshare the file.
9. You get the message: "Cannot undo sharing - (It is not possible to unshare this document)."
So that means you're stuck an probably need to copy this file to create a new node on which public sharing will work again.