Not the author, but as someone who frequently has to answer this question, I'll chip in:

A mistake is a mistake, whether you have a way to reproduce it right now or not. It's pretty much a given that whatever means you have right now to reproduce the problem will evolve and broaden the scope. Also, if you haven't found a way to reproduce the problem, it doesn't mean it doesn't exist: it takes a lot more effort to prove that it's impossible to reproduce than to simply not being able to reproduce the problem.