jQuery Grid Plugin - jqGrid

If jqGrid row ids (passed as separate id property from json data in server) are different only by case, inline edit is not started properly:

double clicking in second row puts first row in inline edit mode. How to make jqgrid row ids case sensitive ?

Data read from server is:

{"total":1,"page":1,"records":2,"rows":[

{"id":"arvelduste_20seis","cell":[null,"arvelduste seis"]},
{"id":"Arvelduste_20seis","cell":[null,"Arvelduste seis"]}

]}