The initramfs uses a different version of busybox to standard (in package busybox-initramfs) - located in /usr/lib/initramfs-tools/bin/busybox
Running this version of busybox does exhibit the error on a normal server.
Checking the config in the package it appears that CONFIG_FEATURE_TEST_64 is not set for the initramfs version.
The initramfs uses a different version of busybox to standard (in package busybox-initramfs) - located in /usr/lib/ initramfs- tools/bin/ busybox
Running this version of busybox does exhibit the error on a normal server.
Checking the config in the package it appears that CONFIG_ FEATURE_ TEST_64 is not set for the initramfs version.