Comment 7 for bug 1780775

The patch attached to this comment fixes the undo/redo bug described above.

This is not a permanent fix, but a temporary fix (see comment in code to that effect) which suggests where the actual source of the problem may be found; it would probably be obvious to someone familiar with the Inkscape codebase.

This patch, and the bug that it addresses, are entirely independent of the two patches previously submitted above.