Is <> A Fluid Source Always Returning False

I've used a modified version of the "check for block in 6x6x6 cube" procedure template to make a sort of lava sponge. However, the sponge is only supposed to change its state to "wet" when it removes a source block, which I'm checking for using the "is <> a fluid source" procedure block. But it always returns false.

Picture of my procedure: 

https://imgur.com/a/TS23g77