If you modify records of an editable grid with paging and if you then page-out, your changes are lost. Well, they are not lost in fact unless you have set pruneModifiedRecords:true on the strore. The modifications are still available so we just need to apply them. Here is the code fragment that does it:

var grid = new Ext.grid.EditorGridPanel({
    store:new Ext.data.Store({
         listeners:{
            load:{scope:this, fn:function(store) {

                // loop through modified records
                var modified = store.getModifiedRecords();
                for(var i = 0; i < modified.length; i++) {

                    // see if we have a record with same id 
                    // and apply changes if yes
                    var r = store.getById(modified[i].id);
                    if(r) {
                        var changes = modified[i].getChanges();
                        for(p in changes) {
                            if(changes.hasOwnProperty(p)) {
                                r.set(p, changes[p]);
                            }
                        } // eo changes loop
                    }
                } // eo modified loop
            }} // eo load listener
        } // eo listeners

        // rest of store configuration

    })

    // rest of grid configuration

}) // eo grid

pruneModifiedRecords must be false (the default) for this to work.