I have imported 50 items from CSV, created invoice and them removed all data including invoice, client, inventory. While inventory list is empty and there is no single catalog created when I start new invoice or new purchase order some mysterious inventory items appear on the list and there is no way to remove them.
it seems like the items are orphaned and don't belong to a catalog. I currently don't know how this happened but here is a way how to get rid of them.
Create a smart catalog and try to list all items. For example: price is greater or equal to 0. Select the smart catalog. The orphaned items will be listed too. Select and delete the items. They will still appear after you delete them until you close and reopen the main window.