jQuery Grid Plugin - jqGrid

After upgraded from v4.3.3 to v4.4.0, the summary will trigger 'this.st.toLowerCase is not a function' on line 11219 in firebug, please see the configuration below. the console log saying that 'this' is a function not an expected string.

confg.:

groupingView: {groupField: ['grpfield'], groupDataSorted: true, groupCollapse: false, groupText: ['<b>{0}</b>'], groupColumnShow: true, groupSummary: [true], showSummaryOnHide: true}

den