Since I didn't know what the item ID for the Command Block in Minecart I started guessing IDs and when I tried the give command with ID #427 the game crashed with a NullPointerException on the item name but tried to give block 0. It's hard to explain so here is the crash report in text format:

---- Minecraft Crash Report ----
// I blame Dinnerbone.

Time: 28/09/13 10:36
Description: Adding item to inventory

java.lang.NullPointerException
at zi.g(SourceFile:151)
at zi.i(SourceFile:171)
at vd.a(SourceFile:234)
at tq.b_(SourceFile:199)
at vf.r(SourceFile:436)
at vf.e(SourceFile:428)
at pb.h(SourceFile:1194)
at vf.h(SourceFile:211)
at kq.i(SourceFile:204)
at kv.a(SourceFile:201)
at gs.a(SourceFile:136)
at eb.b(SourceFile:63)
at kv.e(SourceFile:69)
at ky.b(SourceFile:40)
at box.b(SourceFile:83)
at net.minecraft.server.MinecraftServer.u(SourceFile:494)
at net.minecraft.server.MinecraftServer.t(SourceFile:411)
at bou.t(SourceFile:121)
at net.minecraft.server.MinecraftServer.run(SourceFile:346)
at jc.run(SourceFile:582)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Stacktrace:
at zi.g(SourceFile:151)
at zi.i(SourceFile:171)

– Item being added –
Details:
Item ID: 0
Item data: 0
Item name: ~_ERROR~ NullPointerException: null
Stacktrace:
at vd.a(SourceFile:234)
at tq.b_(SourceFile:199)
at vf.r(SourceFile:436)
at vf.e(SourceFile:428)
at pb.h(SourceFile:1194)
at vf.h(SourceFile:211)

– Player being ticked –
Details:
Entity Type: null (kq)
Entity ID: 1
Entity Name: tangoman1
Entity's Exact location: -281.37, 64.00, -711.48
Entity's Block location: World: (-282,64,-712), Chunk: (at 6,4,8 in -18,-45; contains blocks -288,0,-720 to -273,255,-705), Region: (-1,-2; contains chunks -32,-64 to -1,-33, blocks -512,0,-1024 to -1,255,-513)
Entity's Momentum: 0.00, -0.08, 0.00
Stacktrace:
at kq.i(SourceFile:204)
at kv.a(SourceFile:201)
at gs.a(SourceFile:136)
at eb.b(SourceFile:63)
at kv.e(SourceFile:69)

– Ticking connection –
Details:
Connection: kv@c35bc2
Stacktrace:
at ky.b(SourceFile:40)
at box.b(SourceFile:83)
at net.minecraft.server.MinecraftServer.u(SourceFile:494)
at net.minecraft.server.MinecraftServer.t(SourceFile:411)
at bou.t(SourceFile:121)
at net.minecraft.server.MinecraftServer.run(SourceFile:346)
at jc.run(SourceFile:582)

– System Details –
Details:
Minecraft Version: 13w39b
Operating System: Windows 7 (x86) version 6.1
Java Version: 1.7.0_17, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
Memory: 63180264 bytes (60 MB) / 161779712 bytes (154 MB) up to 518979584 bytes (494 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
AABB Pool Size: 199 (11144 bytes; 0 MB) allocated, 32 (1792 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Profiler Position: N/A (disabled)
Vec3 Pool Size: 14 (784 bytes; 0 MB) allocated, 3 (168 bytes; 0 MB) used
Player Count: 1 / 8; [kq['tangoman1'/1, l='New World', x=-281.37, y=64.00, z=-711.48]]
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.