Thank you for your suggestions. I have tried to import the file again, but the furniture is still put into the wrong categories. I made sure that there is no version of the SH3F file in %UserProfile%\AppData\Roaming\eTeks\Sweet Home 3D\furniture and that SH3D was closed before I imported it again.

My modifications work fine on all other libraries listed on the downloads page, except for the 3DModels-BlendSwap-CC-0-1.7.1.zip file.

Any other ideas? Thanks.