This repository demonstrates what behavior was changed by rust-lang/cargo#5364 (comment)

~/tmp/foo master* 10s
λ cargo +stable run -p bar --features xyz
   Compiling bar v0.1.0 (file:///home/matklad/tmp/foo/bar)
    Finished dev [unoptimized + debuginfo] target(s) in 0.35 secs
     Running `target/debug/bar`
xyz disabled

~/tmp/foo master*
λ cargo +nightly run -p bar --features xyz
   Compiling bar v0.1.0 (file:///home/matklad/tmp/foo/bar)
    Finished dev [unoptimized + debuginfo] target(s) in 0.37 secs
     Running `target/debug/bar`
xyz enabled

~/tmp/foo master
λ cargo +stable build --all --features xyz
    Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs

~/tmp/foo master
λ ./target/debug/bar
xyz disabled

~/tmp/foo master
λ cargo +nightly build --all --features xyz
error: cannot specify features for more than one package