I have ran into the rather frustrating bug for the house Breezehome where, "After purchasing the Alchemy Lab for the house it can disappear without ability to buy it again." Even though the option of buying the forementioned decoration is available when talking to the Steward, the furnishings never actually arrives at the house. Is there a solution to this bug? Such as waiting a certain amount of in-game days to past, finishing a certain questline, or imputing a Console Command code? I am absolutely annoyed when I enter the house to see only an empty space where the Alchemy Table, the empty chest, and the bookself are supposed to be. I am hoping that there will be a solution to this bug. If worse comes to worse, I might have to bite my lip and just live with it or even start a new save file. I appreciate any sort of help or suggestions.
I too had this same problem. What I did was I deleted all my game add-ons (Dawguard, Dragonborn and Heartfire) and when I purchased the Alchemy Labratory from the Steward again, it fixed the problem for me. After purchasing the Labratory, you should be able to re-download the game add-ons and still be able to use your Alchemy Labratory. Hope this helped.