When I encode using [EAC and] lame 3.92 with the following cmd line opts:

--abr 256 -m s -h --nogap

I get an additional mp3 file

That's because using --nogap changes the interpretation of the rest of the command line. That is, with --nogap all filenames on the command line are assumed to be input files (as opposed to one input, and one output file).

This confuses EAC something chronic; the additional mp3 file is likely to be the result of "re-encoding" the first mp3 file under the mistaken impression that it's a wav file.

If you want to use --nogap, you must do so by running Lame from the command-line yourself, not from EAC. Read that whole thread I linked to for more gruesome details. Edit: Also read this.

Peter