MRC

That could be MCpatcher, i forgot about that =o

Aside from a texture pack, there is no mod in the client.
If a texture pack can be considered a mod fair enough, i just want to make clear that there is no change in the client itself.

Allright, added the crash log.

I've encountered this bug by pure luck, and it is "fixed", so unless it happen again i don't think i can send a crash report about it.

I had this problem in 1.5.1 as well, but on a different level.
My server log was generating 50-100 error messages per second and was entirely unresponsive, the "stop" command and "x" button had no effect, it required a forced process ending in order to stop it.
It accumulated over 300,000 error log within a few hours.
Restarting the server does not fix it.

The server was running on Windows 7 Ultimate with Java SE 7 U17.

2013-04-02 14:03:45 [SEVERE] Wrong location! qd['Cow'/283659, l='Test', x=-1519,
55, y=67,00, z=73,45]
java.lang.Exception: Stack trace
        at java.lang.Thread.dumpStack(Unknown Source)
        at abq.a(SourceFile:504)
        at zv.a(SourceFile:1360)
        at iz.a(SourceFile:508)
        at zv.g(SourceFile:1314)
        at zv.h(SourceFile:1221)
        at iz.h(SourceFile:390)
        at net.minecraft.server.MinecraftServer.r(SourceFile:462)
        at hz.r(SourceFile:255)
        at net.minecraft.server.MinecraftServer.q(SourceFile:397)
        at net.minecraft.server.MinecraftServer.run(SourceFile:331)
        at gp.run(SourceFile:573)

I got the same issue, the arrows just freeze where they spawn (when shot) jitter in mid-air for about 1-3 sec depending on it's normal "air-time", then go back on their normal trajectory.
For me, the bug happened on creative mode, in the Snowy Kingdom Superflat preset after about 2 hours in... i have a feeling time could be the cause.
It was easily fixed by relogging and it did no happen before.
I have no plugins nor texture pack installed.

I hope these extra specifications can help. ^_