When you left click between commands, CC3 repeats the last command. When you right click between commands, CC3’s default behavior is to show a context menu with frequently used commands, as well as the option to repeat the last command. You can change this behavior.
To make the default action of a right button click an autorepeat, click Tools > Options then select Right click repeats previous command
To change the commands on the right click context menu, edit the file rclick.mnc in the System folder with a plain text editor. It looks like this:
Repeat last command:!1
------:
Zoom Window:~ZWIN;
Zoom Extents:~ZEXT;
Zoom In:~ZIN2;
Zoom Out:ZOUT2;
------:
Undo:UNDO;
Erase:|ERASE;
Move, Scale Rotate:|MOV;