keychain password prompt prevents screen lock

I have a standard ubuntu installation with deja-dup running daily and a screen lock.
deja-dup saves to a SMB share whose password is saved in the seahorse keychain.

When I boot my system and log in, and just leave it running, after some time deja-dup starts backing up and causes seahorse to prompt for my keychain password. This prompt prevents the screen from locking automatically. When I enter my password, the screen is locked at once.

In Ubuntu 14.04, this effect was the same - but sometimes the keychain password prompt would even overlay the already locked screen. I have not seen this in 16.04.

I think this is a security vulnerability since this makes the automatic screen lock unreliable.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: seahorse 3.18.0-2ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-28.47-generic 4.4.13
Uname: Linux 4.4.0-28-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Jun 29 20:20:28 2016
ProcEnviron:
 LANGUAGE=de_DE
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: seahorse
UpgradeStatus: Upgraded to xenial on 2016-06-09 (19 days ago)