We have an infrequent issue in which our drawing will become corrupt (for lack of a better word) in which a part reference will just "appear" in the drawing, have a zero quantity but the location of the part reference cannot be found. In the attached file, I have ERASED ALL in both model and paper space, all layers are thawed and unlocked yet if you run AUDIT or check blocks that you cannot delete, you'll see quite a bit of data show up even though this drawing is now empty. If you bring up the BOM for the drawing, you'll see an Item 3 for a piece of PVC pipe that can only be deleted from the BOM by selecting it and deleting it from the BOM menu.
In our working drawing (which I cannot share with you), the part ref will appear only when you attempt to merge balloons or when attempting to add a part reference from the BOM menu. It is only at these two moments are we able to see (if we're lucky enough to find it on the screen) and select the item, but even after selecting it still doesn't register on the BOM. The item #3 as shown in the attached file does not show in the BOM until after I delete all other parts from the drawing. With the populated BOM it shows up as an empty line (doesn't say PVC pipe in the part description) and again has a zero value for quantity.
Anyone know why this happens, steps to avoid this from happening, or how to get rid of them after it happens?