It seems like it is something to do with the UIPanel logic changing, but I found a hack/fix that seems to work. It isn't perfect but at least you can see the AH again.

The simple fix for now is to open Addons\Combuctor\frame.lua and go to line 607. Insert the following line after the SetAttribute line that is there, and the one following it.

Code:
self:SetAttribute('UIPanelLayout-pushable', 5)
Not perfect, but it works for now. Next I will try to figure out how to turn off this damn UI panel mess when you manually position the frame.

BTW, dragging the Combuctor frame away from its docked position doesn't stick, so I think it is related somehow.

Noted. What I actually ended up doing is disabling any of the UIPanelLayout attributes that Combuctor sets when you manually set the frame position, and then reenabling them if you decide to plop it back.