Obviously wrong. ;-) This is kind of apple and orange thing. The analogy you drew here is misleading ;-)
In the case you given, there is no space left for prediction, as the value for $a is SET, CLEARLY SET. What kind of prediction is needed? why any prediction is needed? Why any kind of prediction is allowed?
In the case I gave, i.e. the case which this thread is all about, the value of $a is undef, NOT SET, so there is this wild space left for perl to predict. And as I pointed out Perl does this kind of prediction all the time, when it is reasonable, not when it is obviously unreasonable.