Drop nested Attribute does not work first time

[jerome-obeo]

How to reproduce

1. In a GV diagram, create a Part
2. In this part create an Attribute
3. Remove from diagram the Part => diagram should be empty
4. Drag from the Explorer the Part element and drop it on the diagram.
5. Drag from the Explorer the Attribute element and drop it on the diagram.

Observed behavior

First time the Attribute is dropped on the diagram nothing appears.
When drag and drop a second time the same Attribute element then it appears on the diagram as expected.

SysON_issue_drop_nested_attribute.mp4

Expected behavior

The attribute graphical element should be visible when its element is dropped the first time on the diagram.