If i use subgrid in subgrid in grid then there is border shown in bootom of extended icon.

in line 66 of ui.jqgrid.css:

.ui-jqgrid .ui-subgrid td.subgrid-cell {
border-width:0 0 1px;
}

change it to:

.ui-jqgrid .ui-subgrid td.subgrid-cell {
border-width:0;
}

Sample: