I have a large Cargo.toml that I'm placing in a Docker container and prebuilding all the dependencies. However, at runtime there's still one crate that is rebuilt: tempfile v2.1.4. Turning on logging shows:

INFO:cargo::ops::cargo_rustc::fingerprint: fingerprint error for tempfile v2.1.4: mtime based comopnents have changed: Some(FileTime { seconds: 1468471990, nanos: 0 }) != Some(FileTime { seconds: 1468471990, nanos: 914840077 }), paths are "/playground/target/debug/build/tempfile-1b82f6307d61d5f0/output" and "/playground/target/debug/build/tempfile-1b82f6307d61d5f0/output"

More specifically:

Some(FileTime { seconds: 1468471990, nanos: 0 })
Some(FileTime { seconds: 1468471990, nanos: 914840077 })

A complete log