[prussian]

more likely the libc. I have the same version of GNU date using glibc and this behavior persists, as I would expect.

[cfstras]

ah, that makes sense. Looks like the gdate I'm using only links against libsystem, and I don't have a glibc anywhere. So it's the darwin libc that doesn't have this bug.

Testing with https://hub.docker.com/_/busybox, it seems like musl also has this problem. uclibc is not affected.