bootstrap.py fails with "pop from empty list" when trying to bootstrap cargo >= 0.11.0

[berolinux]

Bootstrapping any cargo version >= 0.11.0 fails with

rand: Resolving dependencies for: rand-0.5.0-pre.2
rand: Skipping optional dep serde
rand: Skipping optional dep serde_derive
rand: Looking up info for rand_core 0.2.0-pre.0
rand: opening crate info: /tmp/index/ra/nd/rand_core

Exception:
 from ./bootstrap.py, line 1244:
 pop from empty list

[donbright]

same with me.
in my case, it's looking for crates-io version 0.18

this comes from the file ./Cargo.toml

  crates-io = { path = "src/crates-io", version = "0.18" }

but the index only shows crates-io versions up to 0.16

in fact, so does the website crates.io https://crates.io/crates/crates-io
it only shows version 0.16

so basically https://github.com/rust-lang/cargo is using versions of things that are not yet found in https://github.com/rust-lang/crates.io-index