seems like there is some rationality within mnlf

"I am a Filipino and I can own an estate in California USA. But Philippines is not sovereign in California. USA is sovereign nation in California. I still need to use my passport and get a US Visa to be able to enter California USA. I cannot just go through the backdoor with my private army and breach border controls of USA for reasons that I have an Estate in California.

It is the same in Sabah. At present, Malaysia is sovereign in Sabah. Although Sulu Sultanate owns Sabah, the people of Sulu still has to pass through border controls, show proper passport and Malaysian Visa to legally enter Sabah. "