I have the Panasonic DMR-EH55 and it runs into that issue also.
First in the set-up it will find the places that have suitable tv guide info an put them in your list, you can pick more than one, but I go with the digital one and on the component input, not the RF. I would assume from your post you have this right.
A couple of times I have had to totally reset the unit, including formatting the HD in it (using its format option), I forget the button combination, but you hold like vol up/down for so long and it really does a hard reset to factory everything will be gone, so before you do it, unless you know all of your setting, write them all down first. After the hard reset, unplug it for at least 30 minutes, they manual says something like 2 minutes but I usually leave it good 6-8 hours, likely over-kill but it seems to work.
Then I verify where time is available on PBS and line that up to get the green check make almost instantly on time, and then the channels and finally the guide info, this takes easily 4-6 days to get back to a full TV guide on Comcast anyway.
If you are not seeing the cable box flipping though channels when the Panasonis is turned off, then either the IR sender is not working, which sounds doubtful since it can change at least to a wrong channel at times leading me to think it usually gets it right and it is not broken.
This issue also seems to clear up with the full system reset as I described (you need to check your manual for the exact hard reset buttons for your unit, but it is on the Panasonic site as well we your manual and on avg.
If it only messes up channels rarely then that is just the nature of the beast it IR senders, so make sure the sender LED is clean (use only a soft cloth) and the IR input cover on the cable box is clean, again, soft cloth only and if needed damp with warm water. I had a fingerprint smudge that was enough to mess mine up.
If it messes up all 3 digit channel numbers then verify you have picked the right entry method for your cable box, like on mine, it will take xxx <enter> but the enter is not required, I get far better operation with out the enter.
I sure wish they still made them, the couple units on the market now with a HDD are pure junk compared to the Panasonic, this is why you can get 4 times the original list price for a good one on eBay still!
My next move is to a HTPC, but it is not nearly far enough along yet to be a part of my home enterainment system, still far more like a PC then a piece of AV gear and who needs all that hassle to watch TV...
One final thing on the TV guide, I do notice that when it is close to DST switching it is pretty much broken until the time changes and we are past the old method, not sure why this is, but it has been consistent every year since the change.
Hope some of this helps, the hard reset has always recovered mine, just a bit of pain putting all the settings back in and finding a time when you can erase the hard disk is the worse for me as I tend to stack up shows on it...
I have a Panasonic Hard drive DVD recorder with the TV Guide feature TV.Last month my listings for the TV Guide
has stopped functioning.The channels are in the guide,but no listings.I've checked and rechecked the wiring,all is OK,but I noticed when I attempted to reset the channels I am asked..Comcast:Greensburg,Comcast: Greensburg Digital rebuild.Any way I tried both and no luck.I also noticed before (when new)I could see the channels flashing through cable box window.Now nothing.
So what do you think..G link or cable box,or even the recorder? Just one other item,when I set the manual recorder,say for channel 310(HBO)sometimes it will record instead, channel 10.I do have the sensor directly in front of of the cable box I.R. sensor.
Any thoughts welcome.