@MWDelaney: Yes. Thats right. There is no problem with new projects, only with existing ones. But Scott’s fix works.
@swalkinshaw Thanks! Worked perfectly.
Here is my version which worked without ssh into the server as we use capistrano for deployment.
1.) Remove “old” package, johnpbloch/wordpress, from composer.json
2.) composer update
3.) composer clear-cache
4.) optionally: remove files from HOME/.composer/cache/
5.) Add “new” package: composer require johnpbloch/wordpress
6.) composer update
7.) deploy new version via capistrano: cap deploy