STILL WORKED FINE IN 1.9-pre1,2
I tested it in 1.9-pre1 and 2, it still worked perfectly fine

-The title is a lot to take in, so use the setup below for the first time.

Because of a previous fix, making signs placed by non-ops lose their NBT data (security fix), now there is a bug that affects already placed signs in a non-cheats world.

• Use this command to get a sign with cheats on (enable cheats through LAN, or use NBT editor)

  /give @p sign 1 0 {BlockEntityTag:{Text1:"{\"text\":\"test\",\"color\":\"blue\"}"}}

• Place the sign above a commandblock (standing or wall)

-create 2 dummy objectives test1 and test2

• set your score for both to 0 or whatever number.

• put this command in the commandblock below and and activate it once.

  /blockdata ~ ~1 ~ {Text4:"{\"score\":{\"objective\":\"test1\",\"name\":\"@p\"}}",Text3:"{\"score\":{\"objective\":\"test2\",\"name\":\"@p\"}}"}

=Review what will happen now:

• The sign will have "test" in blue on the first line, your scores on the third and fourth line.

• Next you close the world, and DISABLE cheats (NBT editor, or using the LAN feature or some other way.)

• Reopen the world in non-cheat mode. Although the commandblock is updating only the LAST two lines, the first one has disappeared as well as the last ones!

Video: https://www.youtube.com/watch?v=icx6-5V2OlA
This explains it really well (no sound)

Partial Log of the Exception:

[17:36:25] [Server thread/INFO]: Generating keypair
[17:36:25] [Server thread/INFO]: Preparing start region for level 0
[17:36:26] [Server thread/ERROR]: Failed to load data for block entity Sign
java.lang.NullPointerException
	at aqn$1.h(SourceFile:99) ~[1.9.jar:?]
	at o.a(SourceFile:156) ~[1.9.jar:?]
	at o.b(SourceFile:124) ~[1.9.jar:?]
	at ev.a(SourceFile:21) ~[1.9.jar:?]
	at aqn.a(SourceFile:107) ~[1.9.jar:?]
	at apv.a(SourceFile:108) [1.9.jar:?]
	at ass.a(SourceFile:306) [1.9.jar:?]
	at ass.a(SourceFile:83) [1.9.jar:?]
	at ass.a(SourceFile:70) [1.9.jar:?]
	at lo.f(SourceFile:124) [1.9.jar:?]
	at lo.c(SourceFile:76) [1.9.jar:?]
	at lo.d(SourceFile:91) [1.9.jar:?]
	at net.minecraft.server.MinecraftServer.l(SourceFile:325) [1.9.jar:?]
	at byn.a(SourceFile:114) [1.9.jar:?]
	at byn.j(SourceFile:130) [1.9.jar:?]
	at net.minecraft.server.MinecraftServer.run(SourceFile:427) [1.9.jar:?]
	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_74]