It's not a major bug (maybe even not a bug at all), but it won't hurt to report it. In RoG worlds created from the seaworthy portal some things that exist in both worlds give SW drops:
- merms drop fish morsels instead of fish
- touchstones drop limestone instead of marble when they break upon resurrection
There are probably more, but those are the ones I found.
kill any merm, use any touchstone