I made a game level that contains a lot of small objects - around 1800. Now I want to join all of them to export in game engine (I want to try use one huge light map on whole level). But when I combine meshes many normals get inverted (there are many objects like simple planes, so simple Ctrl+n has no effect). It`s really hard to invert back all normals by hand. BTW all objects have applied scale and rotation. Sadly, I can't provide the source file or screenshots - NDA stuff.
Is there any way to force Blender to not recalculate normals after combining meshes?