Manual:Action Buffer

Virtually every action performed by the user is stored in an action buffer so it can be undone later with the click of a button.

Except for the text editor all modules share the same action buffer, that means that actions performed in those modules can only be undone by the action buffer in the exact reverse order they were performed, i. e. the last action to enter the action buffer will be the first action to be undone, independently of which module the action was originally performed or the current working module. It is necessary because those three modules operate on the same scene objects.

The action buffer keeps not only the actions themselves but also a short description of every action. If you are unsure about what is the next action in the buffer you may inspect it selecting Edit'Undo Multiple (Edit'Redo Multiple) to access the undo (redo) multiple actions dialog with the description of the actions in the buffer.

Notes
 * The action buffer is cleared when you save the current file to the disc.
 * The actions in the buffer are not saved with the file.