during answering on the answer I found some bugs in addRowData, delRowData and setRowData functions in case of usage of idPrefix option and datatype: 'local'. The functions delRowData and setRowData contain the line
P.S. Tony, some time before I posted some other bug reports with my suggestion how to fix the problems: see here, here and here (I still think that the usage of 'u' as the total number of mileseconds since Unix Epoch is wrong. The value of 'u' should be integer between 0 and 999 and can be used as the part of "Y-m-d H:i:s.u" format). Additionally you still not answered on my suggestion to make columnChooser really resizable. Some small parts of the code are included in the main code of jqGrid, but not the main part or resizing. Please answer on the bug reports.