Not sure if this happens on the PC or PS3 but on the 360 if Proventus Avenicci is out on the huge back porch eating the option to buy housing upgrades is not available from his chat menu - it does return once he comes back inside the main hall. Not a huge issue, but I thought I screwed up by not buying all my upgrades the first time I was asked.

Sounds like oblivion, most named character's would go about their day, if they where eating or sleeping then they would not have the option for services e.g - training etc. Does not seem like a bug then.

Yea I thought it was an issue with the NPC doing an activity like you mentioned but he does have the option if he is inside at the main banquet table eating or upstairs in the back hall reading at the small table. It only seems outside on the porch that he refuses to talk about it. Luckily it's a few minutes and he returns inside so while buggy it's not painful waiting for it.