invisible borders and conditionnal single-column page

Hi, I have two problems.

1. I use tables with spanned cells. When the table is too long, it is cut
into two pages in the PDF.
The problem is that the borders of the spanned cells are not drawn. Have
already encountered this?
Is there an option to managed tables splitted onto two pages?

2. I use fo:region-body attribut: column-count="2" so I get two columns in
my document.
But sometimes, I need to insert a single-column page and I don't know how I
can change my page configuration.

If someone could help me for these two issues?

S. Peyronny