Bug report

The following sequence of steps will lead to a grafted (or copied) subgraph with missing dynamic data sources:

1. Start a graft
2. Interrupt it and rewind the subgraph
3. Resume the graft

If at step (2), the graft had already copied data sources, and the rewind doesn't remove all of them, upon resuming, we will skip copying data sources because of this code

The result will be a graft that seems to be ok, but is missing dynamic data sources.