I was able to replicate both issues and we marked them as defect. I will be working on getting these two fixed in future release.
For #1 - this seem to only happen when the SelectionMode for the layer is SelectionOnly.
For #2 - this seem to happen when the new selection does not include any feature from the other layers.
For the meantime, you can use the EditorWidget, this seem to not have the two bugs that you mentioned, or you can iterate through graphics of each layer and ensure that when graphic.Selected is true, mark graphic.Selected to false before performing new selection.