I have managed to do this multiple times:
while in survival mode, try to break a a creative block with a sign placed on the opposite side of the block. Continue repeating trials as fast as you can, maybe even with enchanted pick, and at some point the sign\picture will fly-off the block.

I also spotted an error in my console, but I don't know if it is related to this issue:
13:12:22 [SEVERE] [AntiShare] Failed to update block after 1000 milliseconds
13:12:22 [SEVERE] [AntiShare] Failed to update block after 1000 milliseconds
13:12:22 [SEVERE] [AntiShare] Failed to update block after 1000 milliseconds
13:12:22 [SEVERE] [AntiShare] Failed to update block after 1000 milliseconds
13:12:22 [SEVERE] [AntiShare] Failed to update block after 1000 milliseconds
13:12:22 [SEVERE] [AntiShare] Failed to update block after 1000 milliseconds

version
15:59:42 [INFO] This server is running CraftBukkit version git-Spigot-866 (MC: 1.5.2) (Implementing API version 1.5.2-R0.2-SNAPSHOT)

version antishare
15:59:53 [INFO] AntiShare version 5.4.0
15:59:53 [INFO] Create social awkwardness for creative-mode players
15:59:53 [INFO] Website: http://dev.bukkit.org/server-mods/antishare
15:59:53 [INFO] Authors: Turt2Live and Sayshal

Wh I don't use 5.4.1? Because with version 5.4.1 released on the dev.bukkit.org I can't place any blocks. I'll report this in another topic.

Closing.

Could not replicate after 10 minutes of smashing into a block.