the grid works only for dragging, not for resizing…; to perform grid to resize event add after line 272:

if (container.attr("grid") || (container.attr("gridx") && container.attr("gridy"))){
   var grid= container.attr("grid")? [container.attr("grid"),container.attr("grid")]:[container.attr("gridx"),container.attr("gridy")];
   container.resizable( "option", "grid", grid);
}

This will be fixed on next release.