Deleted task,but the id of tash can't be recycle

I create a new task and the tash id is one,then I delete the task and create a new task again.Now the new task id is two,not is one.
Is this a problem?I think the id should be recycled if its matched task have been deleted.
The version of GanttProject is “GanttProject 2.8.11 Pilsen (build 2396)”

It works as designed.

I am trying to join the development of an open source software. I want to try this software,but I didn’t find the source code.Could you help me?

You want the first link here.