Sellable/unsaleable switch not working

In a map I am using volcanic bridges to represent cooling lava. whether checked or unchecked the bridges remain sellable after underlord 1 claims it. Two things I am doing that might be effecting this:

1. I am selecting the area as a whole even though only some tiles become volcanic bridges for each tick of the "lava flow" creep.

2. Each one-run-script for "lava flow" has the same area selected to become unsaleable. (as I add more volcanic bridges, I'm just targeting the entire area with the switch).