Multiple stacked panels open when a panel-opening button (Add Variable, Open, Debug) is clicked repeatedly in the Behavior Graph window

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Install the Behavior package (com.unity.behavior)
3. Create and open a Behavior Graph asset (Assets > Create > Behavior > Behavior Graph)
4. In the Behavior Graph window, click the "+" (Add Variable) button on the Blackboard multiple times
5. Observe the Behavior Graph window

Actual results: Multiple panels are opened, each being active having to click somewhere multiple times to get rid of the panels

Expected results: Only one panel is active at a time

Reproducible with versions: 1.0.0 (6000.0.81f1, 6000.3.21f1), 1.0.13, 1.0.16 

(6000.0.81f1, 6000.3.21f1, 6000.5.7f1, 6000.6.0b7, 6000.7.0a4)

Tested on (OS): MacOS Silicon Tahoe 26.5.1, Windows 11

Notes:

• Also reproduces with other buttons in the window (Open, Debug)