If you don't have the data from the first three cases running to a shift register and back through each case, then whatever you have wired to the tunnel in the final case will be what ends up being passed out of the case and onto the While loop.
If you are using the "Use Default if Unwired" option on the tunnel, the default value for that data type will be passed out. This would be a 0 for numerics, and empty string for strings, False for booleans.
If you do have everything wired through shift registers, something strange is going on. try posting an example of what you are doing so we can see it.
Ed