I recently had the same problem and it took 7 months and numerous calls to Citibank to finally rectify the problem! Yes, it is entirely a Citibank problem! From incompetent CSR's and Managers, to outright lies. I had CSR's tell me that the T&C's I printed out when I applied for the card were not correct, CSR Supervisors tell me over the phone that they were instituting an investigation and noting that on my account. I would call back later and NO ONE could even find any information or notes on my account about an investigation. That happened 3 different times and the Supervisors assurred me that they would take care of the problem each and every time. I finally got Citibank to post the miles, after I threatened legal action and stated I would report Citibank to my State's Attorney for Consumer Fraud.
My february Citibank statement showed the spend plus purchases posting to my AA account, yet only the spend miles showed up. It wasn't until September of that year that the 20,000 mile bonus finally posted!
My advice, keep copies of your applications including the T&C's, you may need them and keep hounding Citibank, because that's where the problem lies.