Last week, I submitted a glitch that I encountered that ended up with me getting my nautical level boosted to 70 and my nautical experience is at (10306/4200). I submitted a bug report, but was told to also post the bug to the forems. This happened whilst I was f2p, and just sinking cutthroat ships without boarding. I have no Idea what caused it, so I don't know if this can be replicated.
(I will not be opposed to keeping the boosted level, but you may still want to fix this.)