I was intrigued by this, as I often worry about the same thing. So I tried it - entered an item, changed "stock" to "1", then entered the item in the "sales window", and printed a receipt without finalizing the transaction. I even started a different transaction. Then I checked the item in the "Product" section, and the "stock" was unchanged (still "1"). In the "sales window" the transaction showed up with "no" for "paid", since it hadn't been finalized.
Then I wondered if it had been put on layaway, and did that. The "stock" value went to "0", as I'd expect.
We've been using this system for a good couple years now, and I can't say we've had anything like this. We've had other oddball things happen, but nothing that usually seems reproducible (i.e., meaning someone just screwed up). I'll be interested in hearing what the outcome of this is!