Signs disappear from overworld

I HAVE USED THE SEARCH FUNCTION, if this is a duplicate, the search function is not effective.

Upon loading a world, all existing signs' textures are completely gone, leaving only the hitboxes.
On trying to place a new sign, the GUI that appears is missing the entire sign and does not show any text input.

Video proof/demonstration: http://youtu.be/8sas5s5UmpY

Note: After restarting my Minecraft, signs seem to work again, but this is not the first time this has happened.