In the screen shot example the last segment I placed was the segment to the right of the main wall, though I've reproed it in many configurations where you wouldn't collide with the 1x1 wall that you place, but when it connects it makes bigger collision boxes.

Looks like 17 is now using keycode for modifier detection instead of keysym. Based on xev output on my desktop, keycode is 66 for caps, 37 for left ctl and keysym is 0xffe3 (XK_Control_L) for both keys when caps is mapped to control.