As far as i understand, the vertical and horizontal guidelines near the edges of the pages in the tiled PDF are the lines where the pages will be cut after printing.
If this assumption is correct, then i think that the right and bottom lines are not placed correctly. The bottom line should be moved further down and the right line further to the right.
I have attached a pdf as an example. You can see on the first page that the pattern lines are crossing those guide lines. They should stop right when meeting those guide line.
For this test i've used the newest code from the develop branch on an ubuntu 16.04. In the layout dialog i've set all fields values to 1cm to have a margin on each page of 1cm (and therefore to have those guide lines at 1cm from the edge of each page) and selected the paper format A2.