This is the default behavior of the CKEditor. In order to fix this you need to add something to its configuration file which is not possible since you don’t have a local copy but you are using the version from infrastructure.
However you can use this module https://www.drupal.org/project/nbsp This is a known issue in Drupal and the community have created a module for it.
Ah i see, is it a fix that would eventually be helpful for the CERN community ?
I installed the module you recommended but unfortunately the issue is still here. Checking or not the “Cleanup NBSP markup” doesn’t change anything, non-breaking space are still inserted by default.