I am a long time user and an architect. The bug occurs infrequently, and I cannot replicate the bug. I attach a picture. The resulting shape always has the tapered links (in this case, walls as a component and distorted) that lead to a portion of the model (in this case, a door frame as a component) that remains true to the original shape.
Actions are not undoable if they are not recorded by the operation that triggers them. Whatever operation caused this was probably not expected to create entities at all, thus they are not undoable.
I found such problems happen when I either worked with very small entities or with very large complex faces (boundaries with small edges or many holes) with many glued-to components. I suspect it could be an accuracy issue (some vertices fall out of the internal tolerance forcing a face to become tessellated). I would try a validity check (“Fix Problems”, paste in Ruby Console: Sketchup::send_action(21124)).
Or if it was a plugin, it may have aborted inproperly without cleaning the undo stack.
Autosave is enabled. I have a Redner extension, but it was not running at the time. At no time during this bug was the render running. I do have and was working with active components from Flex Tools at the time. Another member suggested Flex Tools was reported in previous posts on similar bugs.