I had the same problem, but I found that you need to set these settings explained in the taskbar3.txt file:

TaskBarTButtonL
TaskBarTButtonM
TaskBarTButtonR

The L,M,R indicates Left, Middle,Right mouse button. There are 3 settings available:
.ontop
.select
.menu

The default Left mouse click option seems to be .select instead of .ontop which is why your taskbar reacts the way it does. Use these settings in your step.rc:

TaskBarTButtonL .ontop
TaskBarTButtonM .select
TaskBarTButtonR .menu

That should make it react how you want