...or is it just me?
when blending 2 objects with a spot color assigned, the blends will not be the spot color.
or...
when you have objects blended you will open up the file later and the blended objects appear to have a color assigned from the Document color pallette
If I blend two rectangles with fills of the same spot colour, all the blend objects have the same spot colour.
If I blend two rectangles, one with a spot colour and 100%tint, and the other , the exact same spot colour but 10%tint, all the blended objects have the smae spot colour but differing tints as you would expect.
If you blend two different spot colours, then the blend objects would have to be CMYK, as there wouldn't be a spot colour to match for each step in the transition.
And its isn't the case that the colour of the blend objects will be from the Document Palette, the blend object colours will have been added to the document palette, thats how the Document Palette works.