AutoCad :: Corrupt DWG Exports From REVIT?

I have a problem with a laggy autocad file that has been created from revit. Basically, what I have done is exported the revit title block to autocad so I can use it in dwg’s, hence keeping all of our drawings looking the same across the project. A little further down the line I have noticed a few anomalies when working on this revit-born dwg…

Firstly, the smallest (but most annoying!) thing is that when working on the drawing, selecting and deselecting ANYTHING will result in a half second lag. The program simply freezes for half a second.

Secondly, I notice that snaps are hindered, cad not recognising intersections and endpoints etc showing that ‘fragmented’ looking icon you see when snapping at a funny angle in 3D. Flattening does not vet this problem either. I picked up a lisp some time ago that takes a more forceful approach to flattening, which worked at first but then two days later the problem recurred, obviously where I had added to the drawing.

Thirdly, I duplicated this cad file and worked on them both for a period of time, then tried copying & pasting at 0,0 world coordinates from one drg to another only to find the copied items disappear! Deleted absolutely everything in one of the files, re-pasted and zoomed all in a bid to find the lines but still nothing until I use qselect to indirectly select them.