Perhaps allowing it to be an object rather than an array would do it, so you could have { '10':10,'20':20,'50':50,'All':-1 }. My gues is the only thing that would need changing is the bit that builds the in the pager.
I can confirm that this is happening to me to in jqGrid 3.8.2. Also, sometimes the data is not displayed after clicking the expand button even if there has been no search. Clicking the collapse button, then expanding again displays the data.
