Description Pierre-Charles David 2015-08-25 10:39:20 EDT

+++ This bug was initially created as a clone of Bug #443385 +++

For sequence diagrams, the documentation clearly says : 

"...IMPORTANT WARNING: To work correctly, Sirius sequence diagrams must have a tight control on where the graphical elements are placed on the diagram and on their synchronization with the underlying semantic model. This means that to use sequence diagrams you must:
* Disable the _Snap to Grid_ and the _Snap to Shapes_ behaviors. For an existing diagram, this is available in the _Rulers & Grid_ section of the _Properties_ view when the diagram itself is selected. You can also disable it for all future diagrams in the preferences: _Sirius > Sirius Diagram > Rulers and Grid_, un-check the _Snap to grid for new diagrams_ and _Snap to shapes for new diagrams_ check boxes."

It will be better if these preferences are ignored for sequence diagrams. A good hint fot that is probably org.eclipse.gmf.runtime.diagram.ui.internal.ruler.SnapToHelperUtil.getSnapHelper(GraphicalEditPart).