Please phone this in and talk to support. I'm sure they can help you. I would ask for escalated support.
The WRT is a temporary solution I would try since this may take longer to fully identify your problem and if it's deemed a FW issue, it would take some time to get it fixed and possible sent to you. So thats why I suggested trying WRT in mean time. However I would wait until you get in contact with D-Link support on the phone as soon as you can.
I've asked D-Link to review this thread.
The WRT FAQ I wrote up yesterday is step by step and if followed, will result in getting the router loaded correctly with WRT and not bricking the router. I didn't brick my 890L.
It would be helpful to let us know what your network topology is like as well. Help us with figuring out whats wrong. More info we have the better.