I don't think this is a bug, as you describe it. The Divine-System is rather complex. Who becomes your Divine is more based on the decisions in your playthrough than who you decide to support.
The major decisions in your playthrough in the story missions and also how and if/how often you talk to the characters in question have more weight then who you support in the war table mission.
In fact, the war table mission is a pretty minor part of the game.
The way this works is, that all your actions shape the world which then votes the Divine most fitting for your world state and YOUR decision who officially to support on the war table just puts the Inquisition in the respective place towards that Divine, which will then be presented in the Epilogue. It's a magnificently complex system and I really admire what Bioware has done here.
Heavy Spoilers ahead:
If you supported the Templars or the Mages is one of the most important decisions, it also plays a role how you position yourself in talks with people around in the game, if you chose to excile or work with the Grey Wardens, etc. There are several sites on the internet that have the details about what decisions people made in their playthroughs on what stages and which Divine they ended up with.
Example of my playthrough:
- I played a Dalish/Mage Inquisitor
- I didn't romance any of the Divine candidates
- I supported the Mages
- I talked a lot with Cassandra, little with Vivienne and through accident, totally ignored Leliana throughout Haven, so I only talked to her since Skyhold.
- I put myself in a position not to be the Herald of Andraste and was rather hesitant throughout the game to accept Chantry Lore
- I didn't go hard-line or Anti-Chantry, but I went anti Circle a lot in the various dialogues throughout the game
- I accepted the Wardens into my Service
- I didn't judge any Mage brought before me in Skyhold to become tranquil
- I encouraged Cassandra to become Divine and told her I'd support her
- I did encourage Leliana to become Divine
- I didn't encourage Vivienne to become Divine, but talked to her about Cass being a good Divine & she agreed
- I supported Cass on the war table.
Outcome:
My first outcome was Leliana (hardened) to become Divine.
Just to explain that briefly: The way you encourage or discourage Leliana on things and possibly also the decisions regarding Leliana in previous playthroughs/in the Dragon Age Keep make a difference to her personality. She can be 'hardened' or 'softened' - and depending on which Leliana you ended up with, that's due to change the epilogue and her actions as Divine massively if you end up with her.
I aimed for softened Leliana but was unable to get her to that point, wether this is because I missed some Dialogue option in Haven (which I know I did) or because she has some pre-installed allignment through my decisions in previous games/Dragon Age Keep is unknown to me.
Anyways, allthough supporting Cass on the war table, I ended up with Lil.
My second outcome _in_the_same_playthrough_ was Cass.
How come the same World State ended up with another Divine?
The only thing I can reckon is, that, while making the same decisions as before, I had missed out some personal dialogues with CAss, previously when Leliana ended up being my Divine. I went back to a Save file in which I had made all story relevant decisions, BUT I followed up with Cass' personal dialogues and got, yet again an option to raise her affection towards me AND I could be supportive towards her being Divine _again. I asked her if she _wanted_ to be Divine and she replied with: 'All I want is a better world, how could I turn down the opportunity to shape it? I would betray myself by not wanting this' (along the lines of this, anyway.
I know that Cass can be your Divine for other reasons and if you never became friends with her and didn't back her on the war table, she will lead on the Chantry and the epilogue will say, that the Chantry is on good terms with the Inquisition at first, but then quickly cuts their ties with the Inquisition. IF you are good friends with Cass, the ties won't be cut if she cbecomes Divine.
You can search for this topic on the internet and will quickly find guides on other forums and sites which go into more detail. It makes perfect sense if you want to find and compare the various finds of other people and diverse playthroughs. The Community is rather eager to find out what decisions exactly give you the Divine you want for your playthrough & world state. But I hope my little rambling & explanation helps to understand that it's not that final action on the war table that makes the difference.
I think it's really fun to explore the Divine-System! It's one of the features where _your_ playthrough and _your_ world state can differ a lot from those of other players, which makes you get the feeling your decisions and actions really shaped your world of Thedas and make a difference. It would be sad imho if a decision as important as who becomes the new Divine would be solved through a simple war table mission.
