When a row is in edit mode, the paddings of the cells are decreased. You can override that with a little bit of CSS to get at the original values (note that they are theme-specific, these are for the Default theme):

<style>
    .k-grid .k-grid-edit-row td {
        padding: 8px 12px;
    }
</style>

Another way to do this is to set a height to the row so that it either matches, or is a bit taller than the default height for the theme, for example:

RowHeight="48"

will be the height of the row of the Default theme in "view" mode, so that when the paddings decrease for an edited row, the general row height will still remain the same.

Regards,
Marin Bratanov
Progress Telerik