Custom lava / water flow files cause random pauses in animation

This happens when using a 32x32 texture pack with the lava & water flow animation sheets double wide. The number of frames is quite high (up to 132) and the animation .txt files have been modified accordingly. The animation will play as intended for a few seconds, then randomly pause. Using the exact same .txt files for non-flowing lava (at halved width) doesn't seem to have any problems.