That has been a problem for a long time, not just stuff from blocks that are missing also other things. Our workflow with dwg:s is like this
1. Import the file in draftsight
2. Explode all blocks and resave it as a new dwg.
3. import in a new TBC project and do the cleanup.
4. Compare the data in TBC with the original file (or a pdf)
5. Export as a dwg from TBC.
6. Import in your project.
It takes some time but the result is much better. And we dont get the problems with stuff being left in the project because you have exploded the blocks and then erased the file.
Have a nice day.