It looks like Baikal has 3 shapes:
This one looks OK:
http://www.openstreetmap.org/relation/555716
But there are parts, which I believe are not proper:
http://www.openstreetmap.org/relation/2929543
http://www.openstreetmap.org/relation/2929544
with notes “кусок озера Байкал, обрезанный по границе областей” - I guess admin borders don’t make it separate lakes.
One of the services (most popular), that makes extracts of the Russian regions from the OSM planet, do not include such huge objects if part of it is located outside of the border.
Two additional relations, you’ve noticed, were made as a workaround.
In my opinion, this relations should be removed. But you will definitely meet some objections if you try to delete them.
А у нас могут быть мультиполигон отношение с двумя соприкасающимися оутерами ??
Насколько я помню, если в рамках одного мультиполигона линии соприкасаются, то это считается пересечением (что есть некорректный мультиполигон). А если это два разных мультиполигона, то ничего криминального в этом нет.
Which one do you mean? “Tagging for exporting” is a nasty hack (not a ground truth), maybe this could be fixed on the export service side.
http://gis-lab.info/projects/osm_dump/
Perhaps. I asked service maintainers, but there was no answer.
But you should ask Kostik about this relations it the first place. Because he is the one, who created them, and I can be wrong about their purpose.