Table Sorting not working as expected

I have this code to try and sort the table by lowest price to highest price (the table is populated by ajax).

Heres the sorting code i have

$("#tableid tbody tr")
    .detach()
    .sort(function(a, b) {

        var dataA1 = $(a)
        .find("td:eq(5)")
        .text()
        .trim();

        var dataB1 = $(b)
        .find("td:eq(5)")
        .text()
        .trim();

        return parseFloat(dataA1.substring(1)) - parseFloat(dataB1.substring(

            1));

        })
        .appendTo('#tableid');

However i do have an issue with this that keeps happening

As you can see this is broken. the blank rows do have some text in and is in a colspan 6. What i'm wanting is these to be at the bottom of the table and the results at the top.

Any ideas how to do this?