This is not a bug in the ext4 support in the grub boot loader, it's more of an issue that the update is not installing the new version of the grub stage1.5 and stage2 images. I'm not sure if this an issue of grub-update not doing this when it should or not.
grub-install should copy the latest grub stage1.5 and stage2 images from /usr/lib/grub/i386-pc to /boot/grub.
Just to clarify:
This is not a bug in the ext4 support in the grub boot loader, it's more of an issue that the update is not installing the new version of the grub stage1.5 and stage2 images. I'm not sure if this an issue of grub-update not doing this when it should or not.
grub-install should copy the latest grub stage1.5 and stage2 images from /usr/lib/ grub/i386- pc to /boot/grub.