Im the current version of Factorio (0.15.2) if you set the radar guide to "when placing" mode and then try to either get a new blueprint book or open an existing one, the game will crash and exit to the main menu. This will not happen when in "always" or "never" mode as I have tested this.
FOR THE DEVELOPER: This is the report the game gives.
Error while running event RadarGridGuide::on_player_cursor_stack_changed (ID 29)
RadarGridGuide/control.lua:74: attempt to index local 'book_bp_active' (a nil value)
Hope I could help!
