mAuthor editor makes it possible to block the selected modules in order to prevent them from accidentally changing their position while working with the presentation.
To block a module or a group of modules, it is enough to select them in the "Modules" list on the left side of the editor window and click the closed padlock yellow icon. The module(s) will be now locked and won't change their location on a presentation page. To unlock the modules, simply select them again and click the open padlock icon.
Please note that while the modules are locked it is still possible to change their properties in the "Properties" menu available on the right side of the editor window.