Thinkpad + Thinkpad Pro Dock - bug on second connect to dock

I have a Thinkpad T460 running ubuntu mate 18.10 and I want to dock it to a Thinkpad Pro Dock. With 18.04, everything worked fine. After upgrading to 18.10, the following bug occurs:

- When the system was just rebooted, I can connect it to the dock, everything works as expected.
- When I unconnect dock, `dmesg` will show the following output (shortened):
---------------------------------------------------------------------
[ 1804.851659] thinkpad_acpi: undocked from hotplug port replicator
[ 1807.515673] [drm] Reducing the compressed framebuffer size. This may lead to less power savings than a non-reduced-size. Try to increase stolen memory size if available in BIOS.
[ 1809.181327] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable link training
[ 1809.449988] [drm:intel_mst_pre_enable_dp [i915]] *ERROR* failed to allocate vcpi

---------------------------------------------------------------------
- Whenever I try to reconnect the dock afterwards, the external monitors will not receive any image. I can still move the mouse around on the internal monitor of the notebook, but no UI element on the screen is interactable. It's as if every program was frozen. When I disconnect the notbook from the dock, all the actions I took in between (mouse input, keyboard input) will be handled, as if the system unfreezes. For example, if I have "ping google.de" running in a terminal, the output will stop when I connect and then when I disconnect again I will receive all the output from in between.
Running dmesg after disconnecting again gives the following output (shortened):
---------------------------------------------------------------------
[ 1660.887875] thinkpad_acpi: docked into hotplug port replicator
[ 1661.831397] [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
(this message is repeated about every 2 seconds for as long as the dock is connected)
(notebook probably disconnected here)
[ 1669.643267] thinkpad_acpi: undocked from hotplug port replicator
[ 1669.764567] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to get link status
---------------------------------------------------------------------

For me, it looks as if this is similar to what is described here, although there are some subtle differences: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/1552040
- The initial report does not say anything about using a dock. When I connect an external monitor via mDP without the dock, I can reconnect it as often as I want, there are no errors. Later comments refer to docking stations though.
- None of the workarounds listed in the report work for me (using xorg.conf.d/20-intel.conf and using /etc/modprobe.d/i915.conf)
- There are clear and easy steps to reproduce on my system (reboot, dock, undock, dock). The bugreport sounds as if it was not clearly reproducable.

So: Should I file a bug report about this? Is there anything I can do to fix this / do a workaround? I would really appreciate that, this bug is really annoying as I rely on using the dock for my day-to-day work without rebooting.