If you create an FPP that is reusable, but don't provide an "Administrative title" (which is an optional field) then it will show nothing in the 'Add content' dialog, which makes them pretty much usuable. :-/
Here's a screenshot:

We already dealt with pretty much this exact same issue with the entity label in #2483335: Improved label in File Entity file usage report, so I propose calling entity_label() to get the admin title.
Here's what it looks like after the patch (falls back on title):

The entity label callback code will also come up with something to show even for panes without titles.
Comments
Comment #2
dsnopekHere's the patch! And a screenshot showing that it shows the title if there is no admin_title. The entity label callback code will also come up with something to show even for panes without titles.
Comment #3
dsnopekWill likely use this in Panopoly per #2562157: Can't distinguish reusable content without admin title when previews are in single mode - it ends up being an accessibility and usability issue
Comment #4
cboyden commentedLooks good. It's working as expected. If there is neither a display title or an admin title, what's displayed is:
[Name of FPP type] (id: [id])
which is fine.
Comment #6
damienmckennaCommitted. Thanks!