Loss of partition properties when switching from MU3 to MU4

Hello,

Wanting to update my scores for use in MU4, I realize that the properties of the score coming from MU3 are partly lost in MU4.

Example, $creationDate that I had filled in MU3, I don't see this property in MU4 although it appears at the bottom of the MU4 score page.
On the other hand, it is impossible to modify this variable since it is no longer in "partition properties"

If I create this property by "New Property" and give it a value, we can clearly see this value displayed at the bottom of the page, but then if I go back to "partition properties" this property has again disappeared.