grid.base.js

... ...
              if(this.p.multiselect) {
                     var emp=[], chk;
                     $('#cb_'+$.jgrid.jqID(ts.p.id),this).bind('click',function(){
                            if (this.checked) {
                                   $("[id^=jqg_"+ts.p.id+"_"+"]").attr("checked","checked");
                                   ts.p.selarrrow=[];  //add this
                                   $(ts.rows).each(function(i) {
                                          if ( i>0 ) {
                                                 if(!$(this).hasClass("subgrid") && !$(this).hasClass("jqgroup")){
                                                        $(this).addClass("ui-state-highlight").attr("aria-selected","true");
                                                        ts.p.selarrrow.push(this.id);
                                                        ts.p.selrow = this.id;
                                                 }
                                          }
                                   });
                                   chk=true;
                                   emp=[];
                            }
... ...

jquery.jqGrid.min.js

... ...
if(this.p.multiselect){var za=[],ua;b("#cb_"+b.jgrid.jqID(a.p.id),this).bind("click",function(){if(this.checked){b("[id^=jqg_"+a.p.id+"_]").attr("checked","checked");

a.p.selarrrow=[]; //add this

b(a.rows).each(function(d){if(d>0)if(!b(this).hasClass("subgrid")&&!b(this).hasClass("jqgroup")){b(this).addClass("ui-state-highlight").attr("aria-selected",
"true");a.p.selarrrow.push(this.id);a.p.selrow=this.id}});
... ...

FYI,

http://bbs.blueidea.com/thread-3015563-1-1.html

Bug is only present on jqgrid version 3.8.x   

http://trirand.com/blog/jqgrid.....qgrid.html

category   Advanced>Multiselect

1. check manually the first  row Inv No = 1
2. check all rows with the 'check all' checkbox
3. click on Get Selected id's link  and value 1 is displayed twice

Bye