I noticed in SethBling's newest snapshot review that crafting a larger scale map will cause some sort of odd bug. When you first put a map on your hotbar and select it, there is a weird texture, it looks like coding of the map. You can do this by crafting a new map, selecting the map so it logs the area you're in, then crafting a larger map by surrounding the one you have with paper. Then place the map in your hotbar and select it, and for a split second, you'll see the weird texture.

This is what it looked like for SethBling: https://i.imgur.com/z99ZTPH.jpg

As of 20w07a, it doesn't happen every time, but it can happen.