Hello,
On version 9.0.2, the access rights to validated data took into account the default profile.
In your case, I think you have a profile on the project that gives you the right to create milestones, but checking back to your default profile, which probably doesn't have the same rights, doesn't allow you to modify validated data. That's why you don't have a problem with floating milestones. Validated dates are not taken into account.
Version 9.0.3 corrects this error and only takes into account the profile on the project. So I can only advise you to migrate quickly to this version to solve this problem or to modify the access to validated data on your project.
Regards
Thanks for your help, it works like a charm in 9.0.3 !
