BlockFromToEvent get the block formed

Hello.I've been trying for two days to get the blocks formed from collision between water and lava(cobblestone,stone,obsidian) and to add them in a list then to clear all the blocks.
In 1.8 looks good,the blocks formed have been cleaned without obsidian.
In 1.7 when i try to clear the blocks something like this happens:


From this:




To this after clear(made a huge hole):



My question is: how can i get exactly the blocks formed without this bug happen?

My code is;

Code:

@EventHandler(priority = EventPriority.MONITOR)
   public void onFromTo(BlockFromToEvent event) {
       blocks.add(event.getToBlock());
   }

 

It looks like all you have to do is update your server. If it works on 1.8, use it. There is no reason to stay on an older update (actually, there are even reasons against it.).

 

Ok,i got it.Thank you,but there is a way to stop water and lava for creating obsidian ?