Gantt "Inactive" Tasks

In the Gantt plug-in, marking a task "inactive" from the Advanced menu greys it out on the task list and Gantt bar.

However, once you save and exit the Gantt, it appears nothing happens with that data to retain it, and the tasks are no longer inactive when returning to the plug-in.

Any understanding as to why this is, and what functionality the inactive option does have?

Thanks!