problem with length of first line in grid

Hi !
I have a small problem with the grid.
I create it with XML input and i set the column length with the property
with command style.addRule(.active-column-i, width:j),
but sometimes the first line in grid become shorten this appearence haven't the systematics and then i click on the data into a line the row move and receive the normal length.
help me please how can i solve a problem.

thanking you in advance.