TabPage Click Events

It sounds like you don't have it wired up:

public Form1() {
  InitializeComponent();    
  Tabs.SelectedIndexChanged += new EventHandler(Tabs_SelectedIndexChanged);
}

There are other events that can give you this information as well: Selected and Selecting.

void Tabs_Selected(object sender, TabControlEventArgs e) {
  if (e.TabPage == TaskListPage) {
    // etc
  }
}