Well my 2400 works just fine with 1080i material so I don't know why you've felt the need to tell me that.
Maybe you aren't using 1080 resolution on the display device? Maybe those aren't high bitrate content? Maybe the deinterlacing issues isn't enough visible on the material you have? Maybe the HW just falls back to BOB deinterlace? Who knows. We just don't have enough information from your setup.
Sometimes I just wonder why I keep trying to help users. At least I leave this thread alone.