Users on a Mac computer using Control + Left click to simulated a right click may experience an unexpected drag lock on work items on a collection. An example where this situation might be encountered is when trying to right click to copy the address for the work item.
The javascript framework being used by Rally is not aware of the Control + Click action that the Mac operating system supports and uses this combination to lock the row to the mouse pointer.
The only solution is to use a different right click action.
For example if using a trackpad, use a two finger click action to bring up the context menu.