I became almost crazy during analysing some strange behavior of one grid: the pager layer "danced" to the bottom on every changing of focus from one grid cell to another:
The reason of the problam was that I used height: "auto" parameter in the grid which work incorrect in case of existing the horizontal scrolling bar. I used shrinkToFit: false in my tests. The problem I could see only in IE (I used IE9 for my tests). One can see the demo which reproduce the problem here. You can compare the results with the same table but where height: "auto" are replaced to height: "100%".
Interesting are also two next demos: this works in IE and another one has the same problem as described above if one click on any cell of the grid:
So I suggest another workaround in grid.base.js. One should just use as the height value the "100%" instead of "auto" in the definition of the div.ui-jqgrid-bdiv. I suggest to change the lines 2300-2304 of grid.base.js: