In all my projects I can see the incorrect behaviour that I try to describe below.

Project X has version 1.0.0-SNAPSHOT, project Y depends on project X and it has set: "Build whenever a SNAPSHOT dependency is built".
Project Y is corretly reported in project X "Downstream project".
Project X is updated to version 1.0.0, but its "Downstream project" is not updated, this is incorrect for two reason:
1. at this moment, Y is not a downstream project of X, because it depends on X:1.0.0-SNAPSHOT not on X:1.0.0;
2. in any case, "downstream project" can't contains Y when X is in a release version, because X - Y relation is due to "Build whenever a SNAPSHOT dependency is built".

Worse, when the version of project X is reset to a snapshot one, for example to 2.0.0-SNAPSHOT, project Y si rebuild, but at this time it depends on X:1.0.0, not on X:2.0.0-SNAPSHOT,
I suppose, this is due to the incorrect information on "downstream project".