Thread sorting issue in Thunderbird – incorrect order and date display when grouped by threads

[Alzi]

Hello Thunderbird team,

I’ve encountered an issue with message sorting in the latest ESR version of Thunderbird (140.4.0, 64-bit).

When messages are sorted by Date (Descending) and Grouped by Thread is enabled, the thread view does not correctly reflect the selected sorting order.
Specifically:

• Threads are not reordered according to the newest message within each thread.

• The parent (root) message of a thread always stays in the same position, even when new replies are received.

• The displayed date for the thread does not match the date of the latest message inside the thread.

• Individual messages inside the thread also ignore the descending date order.

Expected behavior:

The main thread entry should represent the newest message within the thread, showing its actual date, and the overall sorting should respect the chosen "Date (Descending)" order.

Here is a screenshot that demonstrates the incorrect order and mismatched dates.

Additional info:

• Version: Mozilla Thunderbird 140.4.0esr (64-bit)

• OS: Windows 10 22H2 (x64)

• Setting: Sort by Date (Descending) + Group by Thread

• Config value mailnews.sort_threads_by_root = false

• Issue persists even in safe mode (tested with all add-ons disabled)

Thanks for looking into this - it seems to be a regression or sorting logic inconsistency when threaded view is active.

Best regards,
Michal

[ADRN]

Same issue!

Additional info:

• Version: Mozilla Thunderbird 140.6.0esr (64 bits) (but existed on my last OS once I installed Nebula)

• OS: Linux Mint 22.2 (x64) (my last OS was on Mint 21.3)

• Setting: Sort by Date (Descending) + Group by Thread
  
  Also: Sort by Read Status + Group by Thread

• Config value mailnews.sort_threads_by_root =??? (I don't know, but the bug appeared when I upgraded to Nebula)

[i3v]

Same here (Thunderbird 154.0, Windows 11).

As an example, this is how a "Sent" folder looks now, with "View -> Sort By -> Date, Descending, Threaded":

Date      ;  Subject;    Body
-------------------------------
2025-12-27;  Thread-4;  Message-1
2025-12-20;  Thread-2;  Message-1
    2025-12-24;  Thread-2;  Message-2
    2025-12-26;  Thread-2;  Message-3
2025-12-23;  Thread-3;  Message-1
2025-12-19;  Thread-1;  Message-1

Personally, I find this misleading and difficult to follow. I don't like that the Date column does not look sorted.

Spoiler

If I set mailnews.sort_threads_by_root = True  (as mentioned here), the same "Sent" folder would looks like this:

Date      ;  Subject;    Body
-------------------------------
2025-12-27;  Thread-4;  Message-1
2025-12-23;  Thread-3;  Message-1
2025-12-20;  Thread-2;  Message-1
    2025-12-24;  Thread-2;  Message-2
    2025-12-26;  Thread-2;  Message-3
2025-12-19;  Thread-1;  Message-1

This is somewhat more consistent, but less useful (IMHO).

What I actually want is:

Date      ;  Subject;    Body
-------------------------------
2025-12-27;  Thread-4;  Message-1
2025-12-26;  Thread-2;  Message-3
    2025-12-24;  Thread-2;  Message-2
    2025-12-20;  Thread-2;  Message-1
2025-12-23;  Thread-3;  Message-1
2025-12-19;  Thread-1; Message-1

That is:

1. The "Date" column is actually sorted.
2. The most recent message in a thread is shown as the "top level" message. Other related messaged shown inside (newest on top).

AFAIU, it is not currently possible to achieve the desired behavior.