I was messing around with the /summon command when I used:
/summon FallingSand ~ ~ ~

so I could make a falling sign but when I did it, it spawned cobblestone stairs instead. so I got the Cobblestone stairs id and spawned it using:
/summon FallingSand ~ ~ ~

and it spawned a falling sign.

This means that those 2 id's have been flipped using this command.

Edit: there is no id with 68, cobblestone stairs are 67 but still this is a bug