bug#37921: date -d "a day ago" differs from date -d "1 day ago"

[Matt Carter]

When I ask date(1) for the date "a day ago", I get a different result from
when I ask date(1) for the date "1 day ago".
The results differ by 3 hours.

If I ask for UTC time, the results differ by 1 hour.

I'm not able to find anything in the manual to explain this difference.
I realize making sense of a natural language specification of a date is 
complicated.  Still, I wonder whether the difference in behavior is intentional 
and if so why.

$ for dash_u in '' '-u' ; do for one in 1 a ; do date $dash_u -d "$one day ago" 
; done ; done
+ date -d '1 day ago'
Thu Oct 24 09:51:22 EDT 2019
+ date -d 'a day ago'
Thu Oct 24 06:51:22 EDT 2019
+ date -u -d '1 day ago'
Thu Oct 24 13:51:22 UTC 2019
+ date -u -d 'a day ago'
Thu Oct 24 14:51:22 UTC 2019

$ date --version
date (GNU coreutils) 8.26
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by David MacKenzie.

If you think this is a bug and you'd like a fix, I'd be happy to supply one.  
Just let me know.  Thanks.

-Matt