software-properties-gtk erases options in single-line software sources, and does not revert them back

Context: I want to add recent debian i386 software to my sources, in order to play with 32-bit epiphany. I don't want to add recent amd64 or x86-64 software, because I don't want to break my 64-bit core system. In addition to making a source, this involves putting a public key into /etc/apt/trusted.gpg.d, for which see:

Question (which will be repeated at the end): should this be reported as a trisquel issue or a debian bug?

$ uname -a
Linux user-ThinkPad-X200 5.15.0-78-generic #85+11.0trisquel24 SMP Mon Jul 24 20:00:10 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

software-properties-gtk can be run either from the command-line or from /System/Administration/Software & Updates

man sources.list tells me that a software source can specify options that limit the packages that are available from it:
deb [ option1=value1 option2=value2 ] uri suite [component1] [component2] [...]

Substantive complaint: When I edit the components of a source in software-properties-gtk, it erases the options.

Test procedure:

1) write this file:
-------------- /etc/apt/sources.list.d/fsmg-bookworm-i386.list --------------------
# deb [ arch=i386 ] https://mirror.fsmg.org.nz/debian/ bookworm main
# deb [ arch=i386 ] https://mirror.fsmg.org.nz/debian/ bookworm contrib
--------------------------------------------------------

2) run software-properties-gtk, as described above
-- result: new window with four tabs

3) select "Other Software"
- list of sources, with checkboxes on the left, including:
https://mirror.fsmg.org.nz/debian/ bookworm main
https://mirror.fsmg.org.nz/debian/ bookworm contrib

4) click the checkbox for ".... bookworm main"
- password request dialog

5) type user's password & click authenticate
- password dialog disappears
- tick appears next to "... bookworm main"

5) cat /etc/apt/sources.list.d/fsmg-bookworm-i386.list
----------------------------------
deb [arch=i386] https://mirror.fsmg.org.nz/debian/ bookworm main
# deb [arch=i386] https://mirror.fsmg.org.nz/debian/ bookworm contrib
----------------------------------
- note that the spaces have disappeared around the options in both "... main" and "... contrib"
-- I don't know whether this is important

6) click Revert
- tick on "... bookworm main" is still there
-- depending on what "Revert" is supposed to mean, this may be a fault

7) cat /etc/apt/sources.list.d/fsmg-bookworm-i386.list
- unchanged from (5) above, consistent with (6) above

8) select "... bookworm main" and click "Edit"
- dialog box, including "Components" containing "main"

9) edit "Components" to read "main non-free" and click "OK"
- there is a source reading "... bookworm main non-free"

10) cat /etc/apt/sources.list.d/fsmg-bookworm-i386.list
----------------------------------
deb https://mirror.fsmg.org.nz/debian/ bookworm main non-free
# deb [arch=i386] https://mirror.fsmg.org.nz/debian/ bookworm contrib
----------------------------------
- note that there is no longer an arch option on the first line
-- this is the behaviour that prompted me to complain
-- clicking revert does not restore the arch option

Question (which is being repeated as discussed): should this be reported as a trisquel issue or a debian bug?