Thanks for replies.
It seems it depends on particular img file with multiple products. Sometimes I didnt even manage to split mapsets by FID, gmaptool crashed or only some were created and there was error. On other img file it was OK, but I wanted to see all map products at once in mapsource so I tried to manually set mapset fid and pid when splitting and sometime it was OK, another time mapsource crashed. So I suppose its not so easy to assign 1 fid and pid to multiple product img file through gmaptool which will be accepted by mapsource