This issue should now be "fixed" for those on Steam and non-Steam users can download the update from here: http://knucklecracker.com/creeperworld2/patches.php
The story is here:
Yes, there is a new 0801 update for CW2. It's an interesting tale...
In 2012 after the release of version 0497 I apparently fixed a "bug" in the creeper logic related to fields. That fix was never pushed out in an update. So the seasons came and went. At the beginning of 2016 I repackaged CW2 to have a captive runtime. That was based on the last source tree, so it had this "fix". This version of CW2 was downloaded by a few folks who had trouble with the old AIR version.
Later in 2016 I released the CW2 anniversary edition. This was of course based on the latest source, and had this "fix". Problem is, some maps (maybe 1, maybe 10... I'm not sure I only know of 1) relied on the old behavior, not the fixed behavior. Map "#2766: The Treasure Chamber" is the map that broke. The reason it broke is because it actually has a tiny flaw in the way the fields are arranged. They allow creeper to leak out. But, this only happens with the "fixed" creeper/field logic. So the author never knew since it worked just fine in the game he had (and nearly everybody else had).
So, since the game spent 99.9% of its life with the flaw, I have restored the flaw. That ensures that the creeper logic is as it was in version 0497 and all of the existing maps will work as intended. It isn't a really large problem, since the game's entire history has been with the flaw So, the prudent course was to restore that behavior and stop calling it a flaw.