Hm, if it's STM's Update() cycle causing the rebuild, is it one of the two "validateAppearance" boolean calls? The only other Rebuild() call in Update() is invoked when the screen size changes. All the Rebuild() methods in Update() only happen when using the Unity editor, to make it easier to preview text.
I could change those Rebuild methods so that they still respect autoRead, but if a mesh is in the middle of reading, it will Rebuild from the same point. But the intention for them is that when editing the Unity editor, changing the inspector forces text to rebuild. So I don't think I should make that a change...
I hope I'm understanding the problem correctly though! I'm not sure what's causing those Rebuild() methods to go off, exactly. Are you resizing the window in Unity or editing STM's inspector?