I don't think the second part is a bug. I did the same thing on my current playthrough; saved Rugan and agreed to sell the chest and split the profit. When I went to the Zhent hideout they also let me in and then attacked. Rugan was tied to a chair and was being tortured, so I assume he told them what he did with the chest and that's why they are attacking.
Any way I've played it I have never been able to access the 'good stuff,' even when I'm declared a friend of the Zhent.
