Definitely worth reporting. 
I don’t know for sure as I am not a game dev, but I like to think of placeables as objects with multiple properties / layers. I think that this is pretty close to how the game engine works. There is first (well, probably not first) the layer that you see - he visible object texture. While we as players use this as a guide for placing, I think it ultimately has nothing to do about where the object gets placed, and where the object actually resides.
Then there is the collision layer. This is what causes you to stop when you walk up to the placable. Evidence of texture versus collision layers is pretty obvious in other places in the game. You see a mountain cliff. But then when you climb, you either climb inside the texture sometimes, or like a few feet off of the texture, climbing on air. These cases occur when the texture layer and the collision layer are not properly aligned.
Beyond these two layers, the rest is PURELY my own speculation on how the object oriented engine works. I expect that there is a kind of structural support layer. This would be the one that establishes the structural integrity rules for whether or not a placable is adequately supported. If this layer’s rules / requirements are met, the object remains. If this layers rules are broken, the object collapses.
My bet is that there is a structural placement layer. This could, technically, be handled by either the collision layer or the structural integrity layer. But because you can experience object placement struggles, and those struggles seem to differ from the later structural integrity observations, I think that placement is handled through a different rules set. Or, a different layer all together. If this is the case, this would explain some of your observations about when it is placed versus what has to happen to cause it to collapse. Also - it explains why sometimes placing large placables (map rooms, shrines, vaults, trebuchets, etc.) can be a pain in the butt.
Vaults do not always need to have perfect 100% foundations underneath it. In fact, when it took more like 125 or so bombs to sack a vault, the ideal placement was to put the vault halfway on T3 foundation blocks, and have at least a corner of it resting on the raw earth. That way you could not collapse the vault by bombing out the foundations alone. The true cost to sack would be the full 125 bombs.
Now that it’s only about 25 or so bombs to sink a vault, the placement tactic above is not really as relevant. Though - you can clearly see first hand how a raiding player would become miffed if you can be sure your vault edge is sticking in terra firma somewhere.
TL;DR: I think that the report is helpful, for sure. And ultimately, it would be best for these kinds of key objects to be “trued up” with the supporting layers matching as close as possible the visible texture layer.
