If you take a look at civilopedia, apostolic palace should become obsolete after discovering mass media, but it keeps going on even after building UN. Isnt that a bug ?

Yep, I had this as well in my current game. Roosevelt built the AP but when I (playing Dutch) discovered MM, even after I built the UN, the AP was still in force...proposing resolutions and voting leader every so often.

I just wiped America out so I assume this has gone away, but that was only a couple of turns ago so too early to say.

doesn't this have to do with how things become obsolete in civ 4? I only played civ 3 a few times before upgrading (I got it for $5.00) but in that game I believe that if anyone discovered a tech it obsoleted the relevant things for everyone. Civ 4 seems different in that things obsolete when you discover them for yourself regardless of anyone else. THerefore if the owner of the apostolic palace has not discovered Mass Media then they should be able to use it.

However, I built the UN which I feel should definitely obsolete the palace which it doesn't.

Things obsoleet as the OWNER of the thing researches it... i.e. this is why you stear clear of Scientific Method when you build The Great Library.

The AI might have it looooong time, but TGL still alive and kicking cause you havent researched it... IMHO Not a bug.

Well, to verify, gift Mass Media to the AP holder, and see if it expires.

In the interim, I'll mark this as not a bug.

Things obsoleet as the OWNER of the thing researches it... i.e. this is why you stear clear of Scientific Method when you build The Great Library.

The AI might have it looooong time, but TGL still alive and kicking cause you havent researched it... IMHO Not a bug.

I am the owner of both AP and UN and it didnt become obsolete, as I remember.

Could you please post a save?