Cannot set ISO below 6400 for Sony A7M4 with gphoto2 --set-config

[andrewyguo]

Describe the bug

When using gphoto2 --set-config, I cannot set my ISO below 6400. If I try, the command succeeds but my ISO is stuck on auto.

$ gphoto2 --get-config /main/imgsettings/iso
Label: ISO Speed                                                               
Readonly: 0
Type: RADIO
Current: 204800
END
$ gphoto2 --set-config /main/imgsettings/iso=6400
$ gphoto2 --get-config /main/imgsettings/iso
Label: ISO Speed                                                               
Readonly: 0
Type: RADIO
Current: 6400
END
$ gphoto2 --set-config /main/imgsettings/iso=3200 --debug --debug-logfile=debug.log 
$ gphoto2 --get-config /main/imgsettings/iso
Label: ISO Speed                                                               
Readonly: 0
Type: RADIO
Current: Auto ISO
END

debug.log
Now, even if I try to set it back to 6400, it is stuck on auto. The only way to switch out of auto is if I manually reset it on my physical camera.

$ gphoto2 --set-config /main/imgsettings/iso=6400 
$ gphoto2 --get-config /main/imgsettings/iso
Label: ISO Speed                                                               
Readonly: 0
Type: RADIO
Current: Auto ISO
END

Name the camera

$ gphoto2 --auto-detect
Model                          Port                                            
----------------------------------------------------------
Sony Alpha-A7 IV (PC Control)  usb:004,005     

libgphoto2 and gphoto2 version

$ gphoto2 --version 
gphoto2 2.5.28.1

Copyright (c) 2000-2021 Marcus Meissner and others

gphoto2 comes with NO WARRANTY, to the extent permitted by law. You may
redistribute copies of gphoto2 under the terms of the GNU General Public
License. For more information about these matters, see the files named COPYING.

This version of gphoto2 is using the following software versions and options:
gphoto2         2.5.28.1       gcc, popt(m), no exif, no cdk, no aa, no jpeg, no readline
libgphoto2      2.5.30         standard camlibs (SKIPPING docupen lumix), gcc, no ltdl, no EXIF
libgphoto2_port 0.12.1         iolibs: disk ptpip serial usb1 usbdiskdirect usbscsi, gcc, no ltdl, no EXIF, USB, serial without locking

To Reproduce
Steps to reproduce the behavior:

see section Describe the bug above.

Additional comments

I have confirmed that the ISO values I am providing are all valid values for my camera.