I try, but it doesn't work.
I create 2 video to show the behavior, in the 1st I use the drop down menu with the numbers, after the deformation the number value remain highlighted and Grid Warp doesn't work (both the 1st time and the effect repeat time), in the 2nd video i use the more/less density grid button and it works. If you see the 1st video in slow motion, when i press "Ok", the deformation grid seems to reset itself before closing the Grid Warp windows.
1.wmv
2.wmv