Here was a weird one! The blum tandem locking device didn't do this, but the Movento one did. The item was placed correctly at the drawer box, but is then duplicated at the product base point.
I opened the dwg files and discovered the Movento drawings had the solid in a block, while the tandem one and all other drawer slide files are just solids. I got rid of the 'nested' block and purged the drawings, the source files and my working drawing hoping that was all it was. Nope. It was still duplicating them.
The duplicate blocks at the base point weren't the same block, but had a "3d_" prefix added to the name of the others. When I open them up there's another block in there with the solid.
There were some other hardware blocks in the drawing with that same prefix, and they all had all caps somewhere in the name. The Movento locking device in the foundation 22.1102 was named "Blum MOVENTO Locking Device...," left and right. I changed the file name to make it "Movento", and changed the F! sheet table name. Voila, duplicate went away. ???
Anyone ever seen this, or maybe know why some of the hardware is case sensitive and behaves differently? It took a couple hours, but i finally got it fixed, it just seems like a strange bug.