It would be nice if the parking lot scrolled independently from the releases pane when it was open. This makes it easier to drag items from one pane to the other.
We currently do have independent scrolling on both areas but we can understand the potential problems which can arise when trying to drag items across panes.
There are a couple things which could help. For the Parking lot, you can expand the amount of space for the Parking Lot by clicking the "<" icon and dragging the edge of the Parking lot out to a desired width. This might help to give you more space to drag items.
If you know the name of the release that you want to drag items to, you can also open the drawer view for a feature and simply type the release name into the release field. This could allow you to quickly move items around.
With these in mind, we're unlikely to make additional updates in this area but we hope that this can at least help.