At least in my case, I don't believe that analog or digital recording modes have anything to do with this. The problem occurs during menu manipulation or changing modes between live video / playback video / menus -- I am not sure of the sequence yet. It does not happen when the remote is not currently being manipulated.
Once in this mode, everything seems normal except the black background to menus (instead of the normal MPEG bulb video) and lack of live or recorded playback -- just black screen when you try. Live video shows normal channel banners, but again, the video is black and no channel audio. Recordings in progress are intact when checked later, at least so far. A simple reboot restores normal functioning, no need to repeat Guided Setup in my situation.
This feels like a timing issue. As you know, you can often see the MPEG background movie come on a fraction of a second after hitting the TiVo button from live mode (for example) as the MPEG playback engine comes on. Somehow the box is wedging in a mode where it thinks MPEG output is in progress but it really isn't.
My box is from new stock within the last couple of weeks, unmodified, running the (c) release. I've seen this blackout effect twice over the last couple of days. Since I've had the box so short a time, I have essentially no experience with it under the earlier (b) release so can't assert whether this problem appeared with (c) or not.