Continuing discussion from Some ideas to improve Plank:
Another (slightly bug) I’d like to add is that under Compiz, the window snapping doesn’t quite work like it does with a MATE panel or other window.
A long-standing problem between major branchs, or only for a specific one?
Under Compiz 0.9, the one that comes with Ubuntu MATE. I haven’t tried it with Compiz Reloaded (0.8). I only started to use Plank on my work computer last month so I have no idea if windows ever “snapped” borders with the dock. 
Interesting. Are you certain snapping windows or wobbly windows is in effect? Not to assume you’re dumb and don’t know your own setup, just wondering how you have 0.9 configured at the moment.
Also, I’m not certain about wobbly windows; It certainly does snapping, but isn’t there a function to invert how snapping works? It’s been awhile since I’ve tinkered in CCSM. 
This particular computer uses a pretty stock Ubuntu MATE Compiz profile, with a few minor tweaks. For reference, it's the snapping windows plug-in (in case you're thinking of "snap" to the edges of the screen):
It works like this with other windows:
But for Plank, it's not in effect:
The dock is set to "Fill" and not auto hide.
I think I know what's happening -- this shadow gives it away:
The window border is actually quite a way up, as I have noticed snapping does happen at a distance from the dock. Plank must do this so there's an area for when an icon demands attention (i.e. Thunderbird gets e-mail). 