libproj9 does not allow installation in foreign architecture

Steps to reproduce:

sudo dpkg --add-architecture armhf
sudo apt update
sudo apt install libproj9:armhf

Or in a more realistic scenario when doing cross-compiling in a docker container through Clickable. Install Clickable¹ and then try this little example project:

git clone https://gitlab.com/jonnius/proj-demo.git
cd proj-demo
clickable build -a armhf

Error:

apt-get fails to install libproj9:armhf with the following error message:

The following packages have unmet dependencies:
 libproj9:armhf : Depends: proj-data:armhf but it is not installable

The package proj-data is architecture independent. libproj9 should not claim that it depends on proj-data:armhf but rather proj-data:all or simply proj-data so it could be installed. Seems like a packaging issue to me.

OS: Ubuntu 16.04

¹http://clickable.bhdouglass.com/en/latest/install.html