It takes two undo/redo steps to undo/redo the duplication of a block stack

Expected Behavior

When you duplicate a block stack and then undo, you should only need to undo once to delete that block stack.

Actual Behavior

The first time you undo after placing a duplicated block stack, it will move the duplicated stack directly on top of the original stack. The second undo actually deletes the duplicated stack.

Likewise for redoing: the first redo creates a duplicated block stack on top of the original stack, and the second redo moves it to the proper position.

Steps to Reproduce

1. Right-click a block stack
2. Click "duplicate"
3. Place the new block stack somewhere (either attach it to another stack, or put it on the workspace)
4. Right-click the workspace and click "undo" (once)
5. Drag the stack that you duplicated, and observe that there are actually now two stacked copies of it
6. Repeat the process, but this time, click "undo" twice
7. Observe that the stack is now properly deleted

Operating System and Browser

All