Selection box (shift+drag) doesn't add to selection

[jkshenton]

If I select one atom and then shift-click&drag, the atoms in the box that gets drawn get highlighted correctly, as if selected. However, if I then click 'Display selected', it only displays my initial selection and it ignores (hides) the newly highlighted ones.

The potential bug might actually be in crystvis-js but the issue occurs in this app so I'm adding raising here for now.