In your colModel options, you can specify title:false like this:
colModel: [
{ name: "Actions", title: false },
{ name: "Type", index: "Type" },
{ name: "ReceiptLoc", index: "ReceiptLoc" }
],
That empty little box you are seeing is the tooltip copy of text in the cell. Your Action column has no bound values in the cell, that is why it is empty.