Forms are part of the HTML spec, jqGrid is not... why would you expect the grid's data to be cached?
That said, if you use a GET url to retrieve data for the grid, certain browsers such as IE will cache the results of the GET. You will need to make the URL unique (for example, by appending a timestamp) in order to prevent data from being cached. Keep in mind, however, that this will not cache the data in all browsers.
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