When I debug VxWorks ethernet driver for at91rm9200, I find that the receive buffer descriptor(RBD) can't exceed 8, otherwise RBNA error will occur. I read your data sheet and the extrra, and the RBD align to 0x40. Your data sheet say the max size of RBD is 1024. After the MAC read 8 RBD, it wrap back to the first RBD although no wrap bit set in the 8th RBD.
It's your chip's bug, isn't it?

Yes, you can only use 8 Buffer descriptor.

It is not due that the RBD and the RX buffers are located in SRAM ?

I'm using a driver where the RBD and the RX buffers are in SDRAM and there seems no limitation.

At least it works with a ping of the death (65000 bytes).