year vs. releasetime

[winxi]

Hi,
when converting from flac to mp3 with ffmpeg, there is an ffmpeg option (in fact the default) to preserve tags. However, ffmpeg seems to write the YEAR tag from the flac file to a RELEASETIME tag in the mp3 file (at least these names appear in mp3tag).
With 'Date' in the indexTags property, MinimServer will index the YEAR tag in the flac-file correctly, but not the RELEASETIME tag in the mp3-file.
Is this a non-standard behaviour of ffmpeg? Should I rename the RELEASETIME tag in the mp3-files to YEAR?

Thanks in advance!