Works for me as expected, a colon is added. (Using current upstream bash-completion master on Fedora 25, but IIRC this is the way it has been for ages and shouldn't be distro dependent.)
- Bug#868813: scp: add colon after compelted hostna... Christoph Anton Mitterer
- Bug#868813: [Bash-completion-devel] Bug#8688... Ville Skyttä