my game freezes heavy lag spikes

Hello,

it seems while I'm sprinting my game starts to freeze the fps won't drop lower though, but this seems to occur only when I'm sprinting close to new generated chunks.

in 1.6.4 I didn't had this issue, but these are very anoying lag spikes I hope the bug gets found.

additional information about my pc:
Windows 7 (64 bit)
java 6 (64 bit)
video card: Ati readon 6850 2GB ram
processor: amd fx 8 cores (3,1ghz)
ram: 16 gb

Minecraft video configuration as default.