[bblough]

I had external display issues as well, with a T440 and an UltraDock under Debian. It was mostly flickering and blinking of the outputs, but occasionally a display wouldn't come out of powersave mode.

You may have already found and tried these possible fixes, but just in case you haven't-

1) There's a firmware update for the docks that is supposed to resolve a number of display issues.

2) It appears that similar issues can be caused by having a defective or incorrectly-sized dock power supply. So replacing the power supply with a known-good and/or bigger power supply might help.

Though, in my case, neither of the above helped. It turns out I had a bad HDMI/VGA adapter. Since eliminating that, I've had zero display issues. But I'm guessing that probably doesn't apply to you, since my configuration is a little unconventional.

Anyway, I hope you find something that fixes it for you.