I bought a Thinkpad Ultra Dock recently, and last week found that whenever I dock either of my x270s, the laptop's microphone stops working.
Turns out, either someone at Lenovo decided that the 3.5mm audio output on the dock should be a headphone/microphone combo jack.
So, if you have speakers plugged into the jack on the dock, the laptop assumes that there is also a microphone plugged in there and just mutes the internal microphone. You can't un-mute the internal mic in software.
wtf.
Anyway. now I have a dock with litterally only a keyboard and mouse plugged into it.
Because my speakers have to be plugged into the laptop itself, and my usb-c -> DisplayPort cable also has to be plugged into the laptop.
The latter because although the laptop has usb-c, the dock doesnt.