When you press Start / Undock and remove your portable computer from the docking station, or port replicator, the computer is put on standby so that it can re-enumerate the hardware.

Your computer does not resume from standby, and may shutdown.

This behavior will occur if the battery power is very low, without enough power to resume from standby.

To workaround this behavior, either charge the battery, or shutdown the computer before disconnecting it from the docking station, or port replicator.