Pages 5.1 - vertical lines in a table

I have a large document that, for regular formatting purposes, is entirely a table. At various points there is a black vertical line that appears on the inside of the right-most edge of the table. I do not know what it signifies, nor how to get rid of it. In one place it appears in a cell which occupies an entire page;

in another it appears over several, smaller, consecutive cells.

Any thoughts on a) how to get rid of them and b) what they are?