Bluetooth icon shows a little lock, and there's no indication of what it means

All of a sudden the Bluetooth icon on the top right notification area shows a little lock icon (see screenshot).
By clicking on the icon, there's no way to figure out what the icon means.
After turning bluetooth off and on, the lock icon disappeared.
Then, no matter whether I turn bluetooth on or off, no matter whether visible or not, the lock icon never reappeared (the bluetooth icon, without a lock, greys out as expected when bluetooth is turned off).

I thought the lock may mean that Receive Files via Bluetooth was turned off in Personal File Sharing settings (see also #958661: that setting should be in the Bluetooth settings), but even after enabling it, the lock was still showing up (until I turned off and on bluetooth). After disabling file reception again, the lock icon did not reappear.

I suspect that the icon appeared because of an attempt to send a file to the computer which was rejected, because it appeared just after that but:
1 - if that is the case, then an indication should be given, e.g. when rolling over the icon or when unfolding the submenu. You should ALWAYS be able to know what the **** an icon means
2 - if that is the case, there should be a way to "dismiss" the notice, other than turning off and on bluetooth
3 - a toast (or whatever it is called) notification should also be shown at the moment the file is rejected

If the lock is instead supposed to mean that file reception is turned off, or that visibility is turned off, then it's not working properly. If it means anything else, it is not working properly either, as I haven't changed any other setting when the lock disappeared.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: bluetooth (not installed)
ProcVersionSignature: Ubuntu 3.13.0-40.69-generic 3.13.11.10
Uname: Linux 3.13.0-40-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.5
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Dec 10 10:45:21 2014
InstallationDate: Installed on 2013-10-11 (424 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
InterestingModules: rfcomm bnep btusb bluetooth
MachineType: Acer Aspire V3-571G
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-40-generic.efi.signed root=UUID=5830b30e-69e8-4bb4-8a2b-bc2b43c7414a ro quiet splash vt.handoff=7
SourcePackage: bluez
UpgradeStatus: Upgraded to trusty on 2014-05-24 (199 days ago)
dmi.bios.date: 10/15/2012
dmi.bios.vendor: Acer
dmi.bios.version: V2.07
dmi.board.asset.tag: Type2 - Board Asset Tag
dmi.board.name: VA50_HC_CR
dmi.board.vendor: Acer
dmi.board.version: Type2 - Board Version
dmi.chassis.type: 10
dmi.chassis.vendor: Acer
dmi.chassis.version: V2.07
dmi.modalias: dmi:bvnAcer:bvrV2.07:bd10/15/2012:svnAcer:pnAspireV3-571G:pvrV2.07:rvnAcer:rnVA50_HC_CR:rvrType2-BoardVersion:cvnAcer:ct10:cvrV2.07:
dmi.product.name: Aspire V3-571G
dmi.product.version: V2.07
dmi.sys.vendor: Acer
hciconfig:
 hci0: Type: BR/EDR Bus: USB
  BD Address: A4:17:31:0D:4A:70 ACL MTU: 1022:8 SCO MTU: 183:5
  UP RUNNING PSCAN ISCAN
  RX bytes:819218 acl:1083 sco:0 events:198 errors:0
  TX bytes:3969 acl:103 sco:0 commands:71 errors:0