here it is a bug report (I think). I didn't find a workaround actually.
version : beta 2
reproducible : yes
browser : FF only (not sure if earlier version than 10.0.2)
context : grid panel with static column. width define and Viewport used.
bug : when I try to resize a column, only header is resized. cells not. If I sort by any one column after resizing, the cells are resized properly.