What is my succession law, exactly?

I'm new to CK2 and I get confused a lot.

I started as Earl of Ulster, and before my initial Earl died, I changed succession law to 'elective'. I made my daughter elected (barely - some mayor almost got elected instead). A bit later she was able to claim the title of Duchess of Ulster.

But then I notice that my succession law is Gavelkind. I said to myself 'This is probably how it works', and continued playing. But then I noticed popups about who supports who continue to happen! And they talk about County of Ulster, not Duchy:

Is this a bug? Or am I missing something here?

It's complicated :)

If you are a count, then the succession laws for your county will apply.

If you are a duke, then the succession laws for counties don't matter to you and instead the succession laws of the duchy are applied.

If you are a king, same thing.

If you are a king, however, you can hold multiple kingships and each one has a different succession law.

If you are an emperor then that one is separate from your duchy/kingdom.

In any case, it seems that you were a count/earl and then become a duke. First you had one succession law then another one.

Gavelkind is fine for small realms. If you change to elective then you have to start giving land to your sons. If you don't have spare counties/duchies then it's not great.

It's not a problem that you lose a title to a sibling. What you can do is hatch a plot to take it back or just revoke it. Since you're probably in a small realm, the negative hit to opinion won't matter much. If you're in a bigger realm then you should go elective or primogeniture.

Succession law can differ on a title by title basis - Your succession law for the Ducal title is Gavelkind, but the succession law for the County is still Elective.