server Is Ubuntu:
wheel@minecraft:/opt/java/64$ uname -a
Linux minecraft 3.13.0-63-generic #103-Ubuntu SMP Fri Aug 14 21:42:59 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

server is running version 1.8.0_45 java.

Other client is mac OS X 10.9.

I placed water from a bucket next to some lava. Not all the lava was converted to obsidian - there were gaps in the water. Moving the water source block still did not update the lava.

After picking up the source from another block, the water did not fully drain away, leaving a checkerboard pattern.

I mined one block of obsidian, placed the water source block in it, and mined the next block of obsidian to allow the water to flow to the lava. It still did not change to lava.

On the other client's screen, all the lava that I had poured the water on was showing as obsidian. one screen shot shows the other player apparently standing on lava.

I stepped into the lava, and the burning animation showed up on my screen, but I took no damage. I was then unable to move. I disconnected and reconnected (without restarting the client). I was still unable to move until the other player threw water at my feet. Then, I could move again.