not reproduced with Inkscape 0.47 r22583 and Inkscape 0.47+devel r8961 on OS X 10.5.8, with default preferences
I tried these steps:
1) open new document
2) draw curve: 'b', drag-click, drag-click, return
3) switch to select tool & duplicate: <space>, <ctrl>+d
4) use arrow keys to move the duplicate path
not reproduced with Inkscape 0.47 r22583 and Inkscape 0.47+devel r8961 on OS X 10.5.8, with default preferences
I tried these steps:
1) open new document
2) draw curve: 'b', drag-click, drag-click, return
3) switch to select tool & duplicate: <space>, <ctrl>+d
4) use arrow keys to move the duplicate path
no crash.