Sortable Portlet Problem

Sortable Portlet Problem

I am having trouble with a layout using sortable portlets in a three-column layout.  The columns are floated.

The third, right-most column works perfectly.  When portlets are are dragged into it the placeholder appears consistently.

However, when portlets are dragged into the left two columns, the placeholder flickers and sometimes does not appear at all.  The sorting only works intermittently.  The performance is worst in the left-most column; it improves with distance from the left margin of the browser window.

I am setting the connectWith property to a class shared by the three container columns.