Thunderbird Redates Email To 31/12/1969 When Moving Or ??

Running XP Pro SP3 on old (P4) box using Thunderbird 38.7.2

Selected "edit" - "find" - 'search messages" with successful results.

In "search messages" results, highlighted desired message (located in "inbox"), selected "move
to" and selected desired folder.

Message appeared in desired folder as null line dated "31/12/1969 7:00 PM"
Other messages in the folder remained unchanged and usable.

Null message can now be moved to different folders but date remains "31/12/1969 7:00 PM"

Further inspection using "edit" - "find" - 'search messages" stipulating date = "31/12/1969"
reveals many messages have been re-dated with same results (blank line and message text
and/or message source not available).

Subsequently updated Thunderbird to 45.3.0 - no changes!