parts of compound path dissapear when erasing

Hey folks, could use some help... I'm working with some artwork I purchased (svg files) and seeing some strange behavior.  They are compound paths (black shapes with transparent background), and I need to erase the edges.  When I do, parts of the design vanish.  It's always separate small components which are not connected to the rest of the design (but only some of them).  It doesn't matter what part of the design I erase.  Ungrouping isn't an available option.  Expanding doesn't seem to do anything.

Any ideas what's going on? If I create another shape and subtract it, it works fine, but that's getting cumbersome.