Sometimes throughout the game, some chunks (groups of chunks) render one version of a chunk. Yet all of them are loading that same chunk and they all keep flashing between many other versions of chunks in the area loaded. Also mobs models grow in size but load wrong (its hard to describe look at the video to get a good look at the chicken.) I am using Romecraft: CORE Version Pre-XV (Pre-15) (GERMANIA) - [32x/16x][MC 1.7.4] texture pack.
There is a video recording I did of me walking through the bad loading Chunks.
I also included a log from the Minecraft folder just in case you need it.
The event happened when I logged in 22:13.
Video Link: http://social.xfire.com/videos/62adf2
Screenshot: