OpenMW-CS: Clicking on a reference in "Terrain land editing" mode discards corresponding select/edit action

To reproduce:

1. Open an arbitrary cell which includes some references in the scene view.
2. Under "Edit Mode" in the control bar, select the "Terrain land editing" mode.
3. Under "Change brush settings", select any brush (ideally, one with bigger dimensions).
4. Use your primary-select key to select some terrain.
5. Now hover your mouse over a reference (e.g., a rock) and try again.
6. No selection is done; the reference "blocks" the selection.

(This also leads to sudden jumps of the tool outline or selection because these are traced down from the position of reference instead of just ignoring it.)