I've seen bases do this when the script sets an initial movement speed for ships (actually I've seen planets do it as well whilst debugging scripts). It seems a script-allocated initial speed can actually move otherwise stationary objects, but since the base/planet isn't allocating any power to movement the displayed movement speed is 0!
Ideally one should never get offered anything but a base placement/construction mission while packing a base, but that doesn't seem 100% reliable.
dave