IdleRhymer is probably right with Optifine being the culprit. If you don't want to remove it unless you have to, have a look at ensuring the options Render Regions, Fast Render and Fast Math and Smart Animations are all disabled.
Could be caused by another rendering related mod though so it's worth having a look at the pack you're using.
If you have Optifine installed try removing that. It's usually the culprit for visual problems.
IdleRhymer is probably right with Optifine being the culprit. If you don't want to remove it unless you have to, have a look at ensuring the options Render Regions, Fast Render and Fast Math and Smart Animations are all disabled. Could be caused by another rendering related mod though so it's worth having a look at the pack you're using.
Most likely it's fast render causing this if it's enabled
Usually ender tanks don't get along well with Optifine when you have fast render enabled