What?
A very quick note on why borders may be misbehaving in SSRS. This note corrects the situation at Design time. This is where you are trying to select a cell to have an outline border but then cells around it without a border. You may find that BIDS or Report Builder (however you're building your report) will apply the border to some cells and sometimes a whole section of the report with just one border???

How?

1. In Design view, click on the first cell (top-left),
2. hold down the shift key
3. and click on the last cell (bottom-right). This selects all cells.
4. Now open the "Properties" pane,
5. find the "BorderStyle"
6. and type the word "None" next to it (as its value).
7. Press the "Enter" key if you need to.

You are now free to apply normal borders to each specific cell.