Undo will not remove some improperly added slurs

In the sample score attached to the original post, try the following:

1. In the second violin staff, select the first note. Change it to an A.
   This provides a reference point for the following operations.
   2. Select via CTRL-Click the two A's in that measure and add a slur from the Lines palette.
      This should work as expected.
   3. While the two notes are still selected, select the two B's in the second measure via CTRl-Click and add a slur.
      This should introduce an error in the line, as four slur anchor points were selected. The result will be several slurs added with one click.
2. Now try to reverse the operation, either via CTRL-Z or the Undo button.
   One (or sometimes two) of the extraneous slurs can be removed in this way.

Afterwards, Undo will go back to the previous edit, which will change the first note back to a C. This should be the beginning of the Undo stack, but there will be at least three slurs remaining, which are impossible to remove via Undo. Also, at this point, the score should no longer be marked as "dirty", but it is in a different state than it was when you opened it.