This has not happened to me once in patch 9. And I use a lot of ambush tactics. However, the spider queen was bugged in such a way that she could do unlimited acid attacks without combat starting, or /her technically having detected me/.

The most glaring example, pre patch 9:

3 goblins stand on a cliff. I shot two. One dies, the other is injured. The rest enter combat, but leave it quickly and heal up.

Patch 9:
3 goblins stand on a cliff. I shot one. Combat is triggered for the next 9999... turns while they proceed to do nothing. (Will reapply buffs and poison, though).

It's been rare that enemies were offscreen for most of the party, but they didn't heal even then.