This may not be different enough than bombers walk through walls thread but these HGs circled through all walls around Guild Ship. The two on the right legitimately pass thru a hole. The other three walk through four walls eventually, right into heart of base.
My guess is that in correcting the issue where pirates stick around the guild ship, the spaces on all sides of the ship have been affected to the point walls can become nonexistent. This would explain most occurrences posted in the bomber thread as well.
I've noticed them walk through walls as well. It proceeded to walk straight through both walls and down the side of the gs, intersecting with that wall as well. Between that and firing much further than they should, I think HG need a serious scolding. (Same fight - notice it firing 12 squares instead of the 7 its allowed, which can outrange a BUNKER!) @Lynsey [Midoki] @Chris [Midoki] this has seriously ruined several defensive designs that otherwise should have worked fine. Please tell me HG are getting a fix with the PH9 update? Or at least that you notice them misbehaving so radically? As a primarily defensive player, its been getting very not fun trying to counter all these HG bugs. This is the second major HG bug and neither seems to have been acknowledged. They're incredibly broken, they're hard enough to counter when they play by the rules. Thieves got a huge temporary nerf when they weren't working right, but HG are much more broken and haven't even gotten a rude look in their direction.
In consolidating (or crossreferencing) threads, I see Barbed had posted a video without description of the very thing. http://www.midoki.com/forum/index.php?threads/heavy-gunner-juggs-cousin.6313/ It purportedly is fixed in 1.9.1 guild ship fixes, so this thread can stop here unless the bug rears it's ugly head again.