Changed the "lef" section of the techfile to cast via geometry in an
obstruction section (other than vias/contacts below m1) to the base
metal layer;  otherwise "lef read" screws up the layers.

sky130/magic/sky130.tech

diff --git a/sky130/magic/sky130.tech b/sky130/magic/sky130.tech
index d358d2a..e027773 100644
--- a/sky130/magic/sky130.tech
+++ b/sky130/magic/sky130.tech
@@ -5839,6 +5839,14 @@
  # NOTE: obslic only used with li1, not obsli.
  obs obslic mcon
 
+ # Vias on obstruction layers should be ignored, so cast to obstruction metal.
+ obs obsm1   via
+ obs obsm2   via2
+#ifdef METAL5
+ obs obsm3   via3
+ obs obsm4   via4
+#endif (METAL5)
+
 end
 
 #-----------------------------------------------------