In the JQuery Grid if you have the following column definition (for example):

[
    {
        "field": "Name",
        "title": "Name"
    },
    {
        "title": "Address",
        "columns": [
            {
                "field": "Street",
                "title": "Number & Street"
            },
            {
                "field": "City",
                "title": "City"
            },
            {
                "field": "PostCode",
                "title": "Post Code"
            }
        ]
    },
    {
        "title": "Contact Details",
        "columns": [
            {
                "field": "Email",
                "title": "Email Address"
            },
            {
                "field": "Phone",
                "title": "Phone Number"
            }
        ]
    },
    {
        "field": "DOB",
        "title": "Date of Birth"
    }
]

When you drag the multi-column header "Address" and drop it over "Date of Birth" the header and it's child columns move as expected but the column headers in the two multi-columns get mixed up.

This only seems to happen when dragging a multi-column past another multi-column in either direction.