Description of problem:
The "undo" button doesn't work after moving a swimlane. It doesn't undo the previous action. Instead, it messes up the process flow. See the attached BP and video.

Version-Release number of selected component (if applicable):
bpmsuite-6.1.0.GA

Steps to Reproduce:
1. Open the attached BP
2. move the orange box at the bottom then click the 'Undo' button
3. The diagram is messed up