If I have a number of objects I wish to select in Powerpoint, I can
CTRL-Right click on the objects to add them together.

However what's happening is that each time I click on something a further
action takes place;  if I select an object with the mouse it will invariably
move the object after selecting it (Ctrl-Z takes me back to where I want to
be).   Most annoyingly - I select a series of objects with a view to creating
a group - each time I click on an object it copies everything I've selected
as well so after I've grouped I have a large collection of objects to delete
as well!   The only solution is to do CTRL-Z after every click.

Any suggestions as to what's going on?  Needless to say the mouse appears to
be fine in all other programs/actions