Rare Islands
From M:TG Archive, a library of Magic: The Gathering information
The Rare cards were printed on a 121 slots sheets. And there was only 117 different rare cards. The sheet was completed with 4 islands, and the packaging process was not able to sort those islands.
There is the same kind of trouble with the Uncommon sheet, 121 slots with 29 basic lands, so there is a lot of chance to get a land instead of an Unco.
And again for the common cards, 121 slots with 46 basic lands !
This problem was solved when WOTC decided to print the basic lands on a separate sheet (it is to say if I remember well for Revised - Rare sheet - an fourth edition for the others).
