This means the browser is supposed to work out where the box would have
gone if it hadn't been absolutely positioned, but that's not well
defined, and the CSS 2.1 spec says the browser is free to make a guess
at this position.
Also, when you absolutely positioned the text area, its taken "out of
the flow" so that the following submit button layout is not affectted
by the position of the textarea.
I see the problem you are having with the form is to get the text
inputs to align together.
Another possible solution is to relatively position the DIV elements
containing your INPUT elements, instead of the FORM. The LABEL
elements define content inside the DIV that affects the flow of
following elements.
Within each of these divs you could absolutely position the INPUT
element specifying both top and left position (preferably using em
units). The positioning would use the DIV container as a reference
point.
For the text area, perhaps modifying the layout so the the "Comment"
text has a BR (break) after and don't position the textarea might work
better.
The submit button afterwards will flow under the text area without
extra CSS for positioning.