I have a reproducible bug. Here is the scenario:
I have a lifetime TiVo Premiere running 20.3.8-01-2-746.
A recording is set from a season pass to record from 7pm to 8pm.
I go into the to-do list, and modify the recording (not the pass) to record longer -- say until 8:30. Appears to work fine.
Tivo does not modify the original recording. It creates a duplicate one-time recording (one check mark) with no name on the same channel that runs until 8:30. I cannot display the details of this stealth recording from the directory or the to-do list. It makes the "tone up" sound, but never displays.
So I end up with a named recording that did not get modified, and an unnamed recording that did -- the recording process takes up both tuners.
It gets worse. If I attempt to record a second show between 7pm and 8pm, Tivo silently cancels the "ghost" recording without notifying me. It does show as "will not record" or "did not record" on the to-do list. Even better, it says "conflicts with 3 shows"! I only have two tuners -- how can it conflict with three shows?!
So I end up with the original recording from 7pm to 8pm, even though I told it to extend, and I am never told that it didn't until I have lost the content. For a while I thought I was going crazy -- didn't I extend this? (Yes, I did.)
This does not happen when I record a show from scratch and specify a longer run time -- only when I am modifying an already scheduled recording.