Scrolling beyond the page size in an infinite scoll grid (using the scrollbar) gets stuck when the loadMask appears. I've seen this behavior only in IE - tried with IE8 and IE9. Other browsers allow the user to pull the scroll bar all the way down irrespective of whether the loadMask is shown - as it should be.

This is also reproducible in the example for Infinite scroll grid at

To scroll beyond this you could release the scrollbar and try to pull it again until you hit the next page buffer load. This needs to be fixed to have a seamless scroll experience on IE.