AFAIK, the order in which these subexpressions are evaluated is not defined. Adding one more operation (more or less any operation, "" or - or sqrt all work) does change the order of evaluation. But in the absence of some rule requiring the second and third operands of ?: to be evaluated after the first one rather than before, that's merely a detail of the implementation. I don't see any rule about it offhand in "conditional operator" in perlop.
in reply to Re^2: Strange Regex Behavior
in thread Strange Regex Behavior