To expand slightly upon kbmb's answer, with my own observations:
1) Overlapping shows on the same channel now use a single tuner (eg, the same tuner). And of course, the only way shows can overlap is if they are padded.
2) At the moment that the first show stops recording, you will see a slight glitch (pixellation dance) in the second show's recording. Typically that's one minute on, but it will be whatever you pad by.
3) If you go to the To-Do List , the second show will show as not recording until the first show has stopped recording. And the Now Playing will not show it as a recording in progress until the first show has stopped recording. Until you are aware of this bug, it will drive you frantic if you're OCD on checking shows in progress.
4) If the padding on the first show completely overlaps the second show, the second show will not record at all, and History for the second show displays "No Longer in Guide" (or maybe "Not Available", one of these two). This happens to me 100% of the time there is a full show overlap, whereas others say it is erratic in behavior. Nonetheless, I have eliminated 100% overlapping recordings until this is fixed. (Which was mainly Sunday night shows, thank you football.)
The bug kbmb mentions about sequential overlapping shows not recording does not happen to me with any regularity or pattern. But some have mentioned it. Note that he is referring to shows that only partially overlap having this problem. A full overlap causes the problem I mention in #4 above.
Anywhere I refer to a second show, this could also mean a third or fourth show if you have multiple pads on sequential shows on the same channel.
What's odd is that these bugs were introduced late last year with one of the first Roamio updates, when they rolled out the "use one tuner for overlapping recordings" feature. And at first, before we knew about the bugs, we were thrilled. But very quickly the bugs started appearing, and TiVo rolled out another update very quickly, that removed this feature. Then in the latest update, the big 20.3.8, it was back in. Probably a code management mistake left it in.
Ok, I think that's it.