<fo:block padding-top="5mm" padding-bottom="5mm" padding-left="5mm" padding-right="5mm" border-color="red" border-style="solid" border-width="5mm"> outputs top/bottom borders, but not left/right borders. They appear if margin-top="0mm" margin-bottom="0mm" margin-left="0mm" margin-right="0mm" are set as well
I think the borders are only clipped in your case. In an example I've just done, the border displayed nicely and as they should be. What's important to know is that the border to the left and to the right is painted beyond/outside the normal content area of the text. If you set margin-left="0mm" you trigger certain rules that make the border appear inside the normal content area. These rules can be found in chapter 5.3.2 in XSL 1.0. If you want me to point out to you exactly why the border isn't shown in your special case, please reopen the issue and attach a full FO file. Your snippet doesn't show the reason why the border isn't painted.
batch transition to closed remaining pre-FOP1.0 resolved bugs