Hi SusieExpTech
A Move option is only for Premier files which use multiple inventoy locations, you can move stock from warehouse A to warehouse B.
MYOB has many issues (aka bugs) in the Inventory module, some have been fixed, many have not. So the cause of the stock issues might be a combination of things, or simply how you are trying to handle it. I would suggest getting a MYOB experienced consultant in to help you sort it out and set up inventory to work the way you need.
Purchasing an Item as X and selling as Y will invariably cause balance issues. MYOB has an autobuild function where you can 'create' Item Y from Item X and if MYOB works correctly it will track that Item X has become Item Y and has been sold, etc. You may want to look into this function.
Regards
Gavin