Kerbal Space Program

See video: https://youtu.be/tMeo25Juetg

In video, two identical ships, "Bigger Thing 1" and "Bigger Thing 2" do not retain the same fuel priority after "Bigger Thing 1" uses the EP-25 to decouple the attached coupler and permanently be free of it. Original fuel priority places tank closer to probe and battery at -10 and tank farthest at 10. A coupler is at the but end separated from the engine by the EP-25 engine plate. After this engine plate is decoupled, priority near the probe core (root) is 0 and priority near the engine is -10. It would seem as if the probe core on "Bigger Thing 2" became root for the combined ship and after separation, the engine on Bigger Thing 1 (or maybe the engine plate) became the root instead of reverting back to the probe core. Staging sequences have not changed, other than having already staged the engine plate, so fuel priorities should remain the same. I tested with smaller tanks and engine plates, but did not see the same problem.