User added a markup to the expense items in a vendor bill, but the Amount field did not update to reflect it.
This is the expected behavior in Core. Markup only adds to the expense amount when you create invoices from the expenses. The vendor bill uses the cost amount of the expenses (Units x Cost Rate), as that is what you have to pay to the vendors. When you bill these expenses to the client, Core adds the markup to the cost amount to determine the charge amount on invoices. Check the Core Help for more details.