I have found this fix in the 1.7.2 patch notes to be incomplete. Although the game does sometimes prevent you from using a newly captured fief to promote a new clan during the temporary ownership given the ruler, it seems to me saving and re-loading the game allows you to give it away to make clan as if it was your fief before the election.
@MArdA TaleWorlds This is a something of a bug report but I also want to discuss it so I'm posting it here. I also think this bug or ability should be changed into a feature rather then being patched as it is useful.
Here I've clipped a couple videos showing this process. I was only after reviewing it and try several times that I learned it was the save and re-load that changed it.
As you see in the second video, although it grays out the new fief initially, after re-loading the game I can use it to make a new clan.
However I think this ability is actually useful and helps circumvent the idiotic AI and the problem of "the game" telling you what the 3 candidates for a fief are. Normally, to creates a new clan you should win the election to own the fief first. However at a certain point the game will often put up three candidates and there's nothing you can do about it. As the human player you can recognize that the AI clans are incompetent to protect even 1 fief and so it is always in the best interest to create another clan rather then doubling (or more) the fiefs of 1 clan. This can be dealt with by simply minimizing your fiefs you own (using them to make clans) and wealth so you should always be on the ballot for a new fief, but this isn't full proof. Also, because of the 500 influence requirement, difficulty find certain wanderers and the time taken to build town upgrades (and the AI not knowing to make them) you can have a situation where you have to retain too many fiefs (for the good of the faction) and are then unable to claim the next one so it is basically wasted.
I like being able to pull one over on my vassals and build my faction how I want it, how about you?!
