It happens when the Pane is dragged and dropped not on the Compass several times, quickly.
The issue is now fixed. The fix is available in LIB version 2018.1.205, it will be also available in the R1 2018 SP2 Release.
The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.