No, it's not an error, but it's a construct that, because of the well-meaning but misguided "optimization", causes the compiler to freeze up, and the OP was asking for ways that Perl itself, such as in the debugger, could help you figure out what was going on. Usually, perl -c is one of those ways, but not in this case.

Brother tye's reply in that thread is an excellent illustration of what I think the problem is.