MightyBOBcnc
Shift+Double Clicking on an edge that is not active and that is already selected triggers a loop selection
If--at the end of running maya_edge_select--we set an active edge, then Shift+Double clicking on an edge that is already selected triggers the loop selection logic because we can't track DE-selections in Blender without creating our own persistent listener. Unless we were to have a modal running during the entire Edit session, perhaps(?), but a full-session modal or a persistent listener are both beyond the present scope of the addon; maybe in the future.
This actually happens with Faces as well. In fact the root cause in the addon code is probably also why #3 happens since we always fire the operator on double click or shift + double click regardless of if the selection changed because the addon doesn't actually monitor the state of selection or the selection history; it only sees the selection history at a slice of time in the exact moment when the operator fires without knowing what came before.