good find, youd think that this card stock difference would have been "discovered" (noted) sooner, as a set collector would have seen the color differences easily with the cards side by side.
I was thinking it was going to be because some of the cards have the ""UNIVERSAL BASE BALL MATCHING CARDS" line at top, but your Burns has enough of the top border to show that it probably isnt from the set.... ???
PS on your cards.....the dotted line on the right side of Burns is missing on 1 variation, that and the blue shadow on ground and line below trees of the Bodie card are the only differences I see with the printing
here are a few scans I have from the set...
