Hopefully S3D already has this feature, but I haven't found it.
If an STL is placed in S3D, then that same file get modified externally, S3D doesn't seem to "know" about the change; it will just show the STL geometry as it was when it was imported, and print geometry that is no longer current. I can see this being desireable in a saved factory file, but while you're working and iterating design changes, having to remember to delete the STL, then re-import it is a bit of a hassle.
Is there some preference setting I'm missing or should this be a feature request? Repetier Host prompts you when a STL file has been modified externally.