Maps go blank after Updateing from 1.6.1 to 1.6.2

I just updated from 1.6.1 to 1.6.2 and my maps that I have completely uncovered has gone blank. That would be 4 maps that I have made and made copies of them and put them in item frames are now all blank and im not sure what to do. This is the second time I have had to redo and re-uncover maps.