Can't un-assign a planet to an item in logistics.

[Kaikura]

Example: I need cliff explosives on Gleba, I go into my Cargo Landing Pad>Add a section and Name it>Add Cliff Explosives to the Section>Add the Section to a Space Platform.
When I hover over the Cliff Explosives in the Space Platform Hub the cliff Explosives will be listed as Import from: Nauvis. If I attempt to de-select the planet from the import from section, and Confirm it, the planet comes right back on the import from line. I can change the planet, but I cannot leave it open ended so my logistics network will fulfill the request from any planet. Is this a bug, or just how the game works?