This is still broken in Ubuntu 18.04.5 LTS / GNU bash, version 4.4.20(1)-release and in Ubuntu 20.04.1 LTS / GNU bash, version 5.0.17(1)-release.
The manual pages for Bash 4.2, Bash 4.4 and Bash 5.0 all specify "Any additional arguments following dir are ignored. (Only bash 4.2 works correctly.)
This is a bug.
This is still broken in Ubuntu 18.04.5 LTS / GNU bash, version 4.4.20(1)-release
and in Ubuntu 20.04.1 LTS / GNU bash, version 5.0.17(1)-release.
The manual pages for Bash 4.2, Bash 4.4 and Bash 5.0 all specify "Any additional arguments following dir are ignored. (Only bash 4.2 works correctly.)
This is a bug.