Very easy to reproduce crash – here's how:
1 Open LibO Calc with a new file
2 Click on Insert > Names > Define...
3 Enter any name into the box, then click Add
4 Select the name just entered
5 Click Modify and experience crash
I can reproduce this consistently on Windows Vista (32-bit) and Ubuntu 10.10 (64-bit).
(The very similar Data > Define Range... dialogue doesn't have this problem.)
*** This bug has been marked as a duplicate of bug 40571 ***