In single player, I was fired at by a skeleton when the game crashed; when I logged in again, that skeleton fired at me once successfully, then next time it fired the game crashed again; here's the crash screen of the 2nd occurrence; full reports of both occurrences are attached.
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Minecraft has crashed!
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Minecraft has stopped running because it encountered a problem; Ticking entity

A full error report has been saved to D:\Users\Christoph\AppData\Roaming\.minecraft\crash-reports\crash-2012-12-17_23.41.59-server.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash

— BEGIN ERROR REPORT 738583d9 --------
Full report at:
D:\Users\Christoph\AppData\Roaming\.minecraft\crash-reports\crash-2012-12-17_23.41.59-server.txt
Please show that file to Mojang, NOT just this screen!

Generated 17.12.12 23:42

– Head –
Stacktrace:
at qz.j_(SourceFile:276)
at yc.a(SourceFile:1319)
at in.a(SourceFile:450)
at yc.g(SourceFile:1297)

– Entity being ticked –
Details:
Entity Type: Arrow (qz)
Entity ID: 796
Name: arrow
Exact location: -100,11, 60,17, 205,15
Block location: World: (-101,60,205), Chunk: (at 11,3,13 in -7,12; contains blocks -112,0,192 to -97,255,207), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Momentum: 0,41, 0,78, 1,32
Stacktrace:
at yc.h(SourceFile:1196)
at in.h(SourceFile:362)

– Affected level –
Details:
Level name: Hamlet
All players: 1 total; [iq['clipka'/489, l='Hamlet', x=-99,63, y=59,92, z=206,43]]
Chunk stats: ServerChunkCache: 772 Drop: 0
Level seed: 4943026449879767519
Level generator: ID 02 - largeBiomes, ver 0. Features enabled: true
Level generator options:
Level spawn location: World: (-248,64,248), Chunk: (at 8,4,8 in -16,15; contains blocks -256,0,240 to -241,255,255), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 46822 game time, 77568 day time
Level dimension: 0
Level storage version: 0x04ABD - Anvil
Level weather: Rain time: 27519 (now: false), thunder time: 153578 (now: false)
Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Stacktrace:
at net.minecraft.server.MinecraftServer.r(SourceFile:744)
at net.minecraft.server.MinecraftServer.q(SourceFile:679)
at bdz.q(SourceFile:117)
at net.minecraft.server.MinecraftServer.run(SourceFile:613)
at fy.run(SourceFile:849)

– System Details –
Details:
Minecraft Version: 1.4.6
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.6.0_29, Sun Microsystems Inc.
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
Memory: 301297976 bytes (287 MB) / 514523136 bytes (490 MB) up to 954466304 bytes (910 MB)
JVM Flags: 2 total; -Xms512m -Xmx1024m
AABB Pool Size: 8035 (449960 bytes; 0 MB) allocated, 7621 (426776 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 71
Profiler Position: N/A (disabled)
Vec3 Pool Size: 1678 (93968 bytes; 0 MB) allocated, 1373 (76888 bytes; 0 MB) used
Player Count: 1 / 8; [iq['clipka'/489, l='Hamlet', x=-99,63, y=59,92, z=206,43]]
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

java.lang.ClassCastException: qn cannot be cast to iq
at qz.j_(SourceFile:276)
at yc.a(SourceFile:1319)
at in.a(SourceFile:450)
at yc.g(SourceFile:1297)
at yc.h(SourceFile:1196)
at in.h(SourceFile:362)
at net.minecraft.server.MinecraftServer.r(SourceFile:744)
at net.minecraft.server.MinecraftServer.q(SourceFile:679)
at bdz.q(SourceFile:117)
at net.minecraft.server.MinecraftServer.run(SourceFile:613)
at fy.run(SourceFile:849)
— END ERROR REPORT f5aba68d ----------