Lava does not flow to a piston removed block.

I have created a drawbridge using sticky pistons.

The pistons are pushing and pulling a block in the Y-Axis.
Place lava source directly next to or nearby the drawbridge.

It should flow properly, however occasionally it will get stuck creating a "Parting Red Sea" Effect with the lava.

This is in a minecraft server 1.6.2, playing in survival mode.