Table wider than it's parent


I have a trouble with table width. Inside this table I have several generated colums (one for the each month) with text field and a button. Text field and button reside on 130 px fixed width horziontal layout and seems like table can not properly calculate the width of itself if it is set to 100%. Here is the code to understand what I’m talking about:

UPD: solved that problem replacing FormLayout with HorizontalLayout, but I still do not understand why FormLyaout behaves in such a way