Same anon here who posted in the "weapon rack bugs" thread. Figured it would be more appropriate to start a new topic for this.
I still haven't been able to purchase Breezehome, but this bug luckily does not extend to other player homes (which I had initially feared), so I was able to purchase Honeyside and was offered to buy the house in Solitude.
As for Whiterun, I've tried everything I could think of short of using the CK. I've reset the main quest (MQ104, NOT MQ106 as it states somewhere!) several times, reset and respawned Proventus, dismissed my follower, etc. Nope. Guy won't update his dialogue. Lydia is sitting in Dragonsreach (which suits me just fine, actually...) and I've got the Axe of Whiterun and the Jarl's approval - it's just Proventus who is bugged. I've been able to purchase Breezehome just fine in other playthroughs previously, but this is my first playthrough after updating to 1.9 in case this may be relevant. I don't know why this would affect Proventus, since the dialogue trigger is set in the same script that gives you Lydia and the Axe of Whiterun, but whatever. No Breezehome for me.
If anyone ever manages to figure this out, please post!
I've had my petty revenge and unleashed a dragon inside Dragonsreach that killed the court mage. I'll be living in his quarters now. Take that, Whiterun!