I've never understood in several years of regular usage and development why Visual Studio Form Designer, hangs out while drawing and adjusting any form generated by itself.

You are forced to modify manually the Visual Basic or C# code in its #Region " Windows Form Designer generated code ", updated at your last successful creation modification.

I needes to add another TabPage in a TabControl, but I forgot to add also in the final part of the InitializeComponent() method these function calls:

    Me.tabFiles.ResumeLayout(False)
    Me.tabFiles.PerformLayout()

If you miss those ones, you are out of luck with docking and control anchoring in the TabPage. At runtime your controls contained in the page won't resize or fit correctly with respect of TabPage borders and you'll get an headache for sure while searching your bug.