This is a bug in jQuery

http://www.trirand.com/blog/?p.....ed-in-ie6/

Regardds

Adding that this issue appears on IE6 and IE7 - but not on IE8

Also:

The original observation of this bug was for loadonce:true.  With loadonce:false, I noticed on IE7, that for search criteria other than the first criteria, the "op" was passed as "undefined".  This seems to be the cause of this issue.  Here is an example of three search criteria where the 2nd and 3rd have "op" as "undefined":

{"groupOp":"AND","rules":[{"field":"type","op":"eq","data":"D"},{"field":"long","op":"undefined","data":"5"},{"field":"short","op":"undefined","data":"10"}]}

For an example see the demo on the jqGrid site - the "New in version 3.7", "Multiple Search" example doesn't work in IE7 when you try and search on more than one field.