Unexpected prefix value

[Pascal Hambourg]

Hello,

Distribution: Debian 12 (bookworm)
GRUB version: 2.06

If I build an EFI GRUB core image with

 grub-mkimage --prefix='(hd0,gpt4)/' --format=x86_64-efi \
  --output=/boot/efi/EFI/azerty/core.efi part_gpt ext2

when booting it, $prefix has the expected value:

 cmdpath=(hd0,gpt1)/EFI/azerty
 prefix=(hd0,gpt4)/

But if I build an EFI GRUB core image with

 grub-mkimage --prefix='(hd0,gpt4)' --format=x86_64-efi \
  --output=/boot/efi/EFI/azerty/core.efi part_gpt ext2

(no / at the end of prefix), then when booting it, the $prefix value 
seems to be the combination of the --prefix device and the $cmdpath path:

 cmdpath=(hd0,gpt1)/EFI/azerty
 prefix=(hd0,gpt4)/EFI/azerty

Is this expected behaviour ?