lightdm greeter not working while in docking station

I'm running a clean install of Xubuntu 16.04 on a Thinkpad X230 and a docking station.

Whenever the login screen comes up -- after booting, by locking the screen, waking up from standby -- as long as I'm plugged into the docking station, the laptop display and all connected monitors just show a blinking underscore and start flickering. It seems like they are endlessly switching resolutions.

I can immediately resolve the issue for the moment by releasing the laptop from the dock -- the greeter pops up and I can login normally. After login, everything works as expected, including multiple monitors etc.

I understand that all relevant logs are added to this bug automatically, let me know if anything's missing!

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: lightdm 1.18.3-0ubuntu1.1
ProcVersionSignature: Ubuntu 4.8.0-52.55~16.04.1-generic 4.8.17
Uname: Linux 4.8.0-52-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed May 31 14:05:16 2017
EcryptfsInUse: Yes
InstallationDate: Installed on 2017-05-14 (16 days ago)
InstallationMedia: Xubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215)
LightdmDisplayLog:
 (II) AIGLX: Suspending AIGLX clients for VT switch
 (II) AIGLX: Suspending AIGLX clients for VT switch
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)