I'm having issues with the buffer of my Tivo HD DVR - THR22-100 - basically, that sometimes the unit is not keeping a buffer. Anyone else having a similar issue? I spoke to someone at DirecTV today who says it's 'known' that this unit may or may not keep a 30-minute buffer, apparently at its own whim. That's not an acceptable answer to me so I'm hoping that someone here my have some insight. Thanks!