Some AutoCAD commands are nonreentrant. These are commands that ask for user input and therefore would normally allow a document window switch, but would cause serious complications if it were switched, or if the command was called again in another document. Three commands fit this profile:
The TABLET command is restricted because the user is defining how the pointing device is going to work, so that operation needs to be finished before anything else can be done. Because NEW and OPEN have to open a window, and then ask for a name (when FILEDIA=0), switching to another window at that moment could be error-prone.