Reproduce:
Create screen with 2 columns and add screen item to last column.
Now update screen with API screen.update method

{
"screenid": "27",
"hsize": 1,
"screenitems": [
{
"screenitemid": "140",
"screenid": "27",
"resourcetype": "0",
"resourceid": "550",
"width": "500",
"height": "100",
"x": "0",
"y": "0",
"colspan": "1",
"rowspan": "1",
"elements": "0",
"valign": "0",
"halign": "0",
"style": "0",
"url": "",
"dynamic": "0",
"sort_triggers": "0",
"application": "",
"max_columns": "3"
}
]
}

keep screen 'hsize' and screenitem 'x' as in example.

Notice:
screenitem is deleted