Simply put: Sector importing does not preserve the connections of rails to storages. This is easily reproducible as well. Just see the "Steps to Reproduce" section. I tested it on a newly created sector export.
I've included a simple sector export here that I used to try and reproduce the bug. This can be used as the basis for your own test if you'd like.
How I know: We have custom quests on our server, which makes use of the /sector_import command and scripting. In one of our quests, we have a randomizer that uses rails connected to storages from one entity to another. A person presses a button, a storage raises out of the floor, and then it pulls items from a random storage. However, it has not been working since the last hotfix, so I checked it out, and I noticed that the rail is not connected upon being imported. I know the sector export is good, since we've been using it for a while now with no issues. This is new as of the last hotfix.