Thanks for joining this conversation about Subtotal, @RangeRover.

The Subtotal functionality not only calculates the Amount column but also the hours and quantity. Since this isn't your case, let's try running the Verify/Rebuild utility. This is a way to check if the unexpected behavior is caused by data corruption.

First, let's run the Rebuild Data utility:

1. Go to the File menu.
2. Choose Utilities.
3. Select Rebuild Data.
   
4. On the QuickBooks Information window, select OK.
5. Select OK when you see Rebuild has completed.

Next, use the Verify Data utility:

1. Choose the File menu.
2. Select Utilities.
3. Choose Verify Data.
   
4. If you see QuickBooks detected no problem with your data, select OK. Then, proceed with creating an invoice with Subtotals.
5. If Verify finds an issue with your data, you will be prompted to Rebuild Now or View Errors. 

Additionally, you can refer to the Resolve data damage on your company file article if you need to perform more steps.

That should do it. Keep me posted on the results or if there's anything else you need. I'm always here to offer assistance. Have a good one!