HDMI without 5.1 may not be a bug. It may be intentional.
Most of the users are connecting STB directly to TV. If Dolby 5.1 is sent over HDMI by default, the TVs should be able to decode/downmix to 2.0.
If the TV cannot downmix, then audio will not be proper for the HD channels. STB is downmixing by default and sending through the HDMI cable. Whoever needs 5.1 can use the Optical cable.
Ideally this should have been an option to downmix or bitstream through HDMI so that user can choose.
The STB may be capable of 7.1, but there is no channel with 7.1 audio hence we cannot test it. Similarly Videocon and TS says 3D capability, we have to wait and see till channels are available.
As you may be aware there are very few movies in Blu-ray with 7.1 Audio.
Mono or pseudo stereo/5.1 audio may not be a TS issue, that may be the way in which they are getting it. Very few non-movie programs are recorded in 5.1, even if they are recorded in 5.1 we may not feel much of effect like movies. Hence I don't care much if Neo HD is not having 5.1 audio.