No, it looks like a small difference between how Excel and OpenOffice work with drop-down menus in cells is causing the problem.  Specifically cells F11, F15, and F19, the three cells where you select the To-Hit values for each battery.  In Excel, when you select a to-hit value, it's displayed as 3+, 4+ or 5+.  In OpenOffice, the selected value gets displayed as 3, 4 or 5 (no plus signs).  This throws off the SU calculations for each battery because one of the formulas used to compute SU does a lookup expecting the 3+, 4+ or 5+.  If there is anything else in the cell (like a 3, 4 or 5), it returns a 0, so you get a 0 value for SU.

The good news is, it's easy to fix.  In OpenOffice all you have to do is change the formatting on cells F11, F15, and F19 to Text.  You can do this by right-click on each of these cells, select Format Cells, and select Text from the options under Category.  Once you do that, the selected values will appear as 3+, 4+ or 5+ and everything seems to work normally.

Based on my testing, if the authors of the construction spreadsheet would be so kind as to change the formating on these three cells in Excel from General to Text, that would fix the problem for any future OpenOffice users that download it.