OK, I've read the FAQ threads, did my homework first before posting this. We have 2006 so layer filters is not the problem. Ran Robert Bells lisp just to say I did. Tried -purging REGAPPS too, there were none.
When the drawing is wblocked the file size shrinks down to ~20Mb, when it is saved_as, it balloons to over 10 times that size.
The properties on both are the same. There are no x-refs or images attached. There is a lot of 3rd party, 3d geometry , though.
Any ideas?