Thanks - there is indeed a bug in the LiveGridView that prevents forceFit, autoFill, and resize from working correctly on it. For now, my suggestion is to properly set the column widths to begin with, and to set a fixed size on the grid instead of letting it resize with the rest of the page. If you do need to resize the page, consider rebuilding the grid to ensure that this issue does not occur.
This has been fixed in GXT 3, and any new project should be started with GXT 3 to get bug fixes as fast as possible. We are working on backporting this fix to GXT 2, but do not yet have a release with it.