Comment 5 for bug 630642

correction: workaround b) doesn't work ;-) -- use this instead:
1) select a path and switch to node tool
2) activate snap target 'to cusp nodes', drag & snap one node to grid
3) deactivate snap target 'to cusp nodes' again
 -> now all dragged nodes snap to grid as expected.

It seems as if parts of the snapping context (snap targets) are not "initialized" in the node tool context when the document is loaded.