If they get damaged in any way, the stop the advance and group up. Meaning you can keep them permanently immobilized until they flee by shooting mortar at them every 10 seconds or so. I know sapper behavior must be difficult to code but the change that was made to make them behave this way made them much less of a threat than they were before.
I think guards who protect the sapper (mining) units should behave much more aggressively and I think the entire raid should ignore mortar shells because stopping after they get shelled is pointless
yep, once you hit one with an Insanity lance and have a few mortsrs they are toast