It might not be a bug, but rather a result of the unfortunate UI.
See the problem is that just because you provide a parameter name for the random seed info does not mean that the particle system also has a parameter set at runtime.
But then what should the result look like when I retrieve a value from the FRandomStream* in the particle module? As long as there is no default value, the behavior is undefined.
By adding an element to the seed array you provide it with a default value and it can be initialized to be used by the particle system in all cases.