"Active (Debug)" versus "Debug"

Active refers to the currently active configuration, there is a drop down list in the standard toolbar that allows you to define the current active configuration, when you change these the "Active" configuration in project properties will change.

The Active tab is to denote the currently active configuration. In the case of Active (Debug) it is noting the active configuration is the debug one.

You can demonstrate this by changing the current configuration to Release and then revisiting the Debug tab. It will now display Active (Release).