The circle file is 3MB because of all the linestyles and textstyles that it mysteriously (to me) drags along with it. These are all from the underlying architectural xrefs (which were not selected!). It is pretty bizarre, since if you do a LIST ALL on this 3 MB file, you get exactly one object.
Select objects: all 1 found
CIRCLE Layer: "de-mducts" Space: Model space Handle = a8 center point, X=950'-8 27/32" Y=54'-9 17/32" Z= 0'-0" radius 0'-3" circumference 1'-6 27/32" area 28.27 sq in (0.1963 sq ft)
The only way I found what was in it was to do a PURGE and look at items that can not be purged (there were NO items that could be purged).
Not sure why wblock ENTIRE would perfectly clean a big pig drawing, and why wblock SELECT would include a 10 ton pile of crap in with a simple object.