I just updated my SMP server (with world resetted) to 15w31a as we always kept with the snapshots, although when I (The Owner) placed a sign I instantly got kicked, can no longer join the server at that and received an error: (Screen Shot below)
http://i.imgur.com/cR2znzF.png
Internal Exception: io.netty.handler.codec.DecoderException:
com.google.gson.JsonSyntaxException:
com.google.gson.stream.MalaformedJsonException: Use JsonReader.setLenient(true) to accept malaformed JSON at line 1 column 2
Linked issues
Comments

Duplicate of MC-82968. Please search before creating new issues.
I am getting the same error, it is NOT a duplicate! please actually LOOK at the report before you look stupid. connecting to certain servers gives an out of bounds index error. something to do with signs but a different problem from before, CLEARLY stated by the two DIFFERENT error messages./

@unknown, what are you talking about? Are you sure you're commenting on the right issue? This issue is clearly the same issue as MC-82968: Same cause, same error message.
I also have this problem. After deleting all the JSON files in my server folder hoping to reinstall them, i also got the error message
"Internal Exception: io.netty.handler.codec.DecoderException: java.lang.IndexOutOfBoundsException: readerIndex(9) + length(1) exceeds writer Index(9): UnpooledHeapByteBuf(ridx: 9. widx: 9, cap:9)"
When i reverted my world back to 1.8.8 all the signs were full of backslashes and quotation marks as well..