Hello,
Your new feature from 8.0.0 with drag&drop of multiple grid’s rows provided also problems with it. Default behavior was changed and now in applications, where selection was enabled and drag&drop feature enabled, it works different.
Previously only clicked row was affected and dragged.
Now, all selected rows + clicked one are dragged. I have very often situation where there is grid and first row is selected by default, but from version 8.0.0 dragging works bad.
Look there: DHTMLX Snippet Tool
try to drag any row another than selected. It works bad because you see two dragged rows despite on fact, that multiselection is disabled.