I came across a problem yesterday, with imported addresses, and I think it's the same problem you're seeing. I brought it to the attention of the devs and they produced a development version of the software which I think will fix this problem. However, it hasn't been released yet, but will be in version 1.9.

My problem was with an imported address which was used in a transaction. The transaction did not get recorded. To fix it, I had to erase my wallet, and then recreate it. Of course, this removed the imported addresses from the wallet, but when I reloaded them, they were correct.

Maybe you can try this, if you're interested, or wait until version 1.9 is released.