I've never seen that, and also never seen an AI actually cave in to territorial demands. Did you have relations with Vichy at +200?
Vichy had none to guarantee there independence so the gave into the claims.
Is that the only thing that affects whether an AI nation will surrender its territory?
No, it might have something to do with the strength of the nation to. Maybe similar to military control.
That would not explain UK accepting to cede territory to ireland. Also there is the unusual case of the european union. It can demand territory by some sucess from all european nations. The issue of demanding territory deserves a thread by its own. Have you ever seen Tibet giving in to demands by China? I have not.