This was the problem, thank you... I was having trouble thinking through some of the escaping. It does need to be [^\\]\/ at the end. For the curious: I am implementing and "ed" replacement that will make use of perl6ish regexen and a number of other features. This is a piece from my grammar parser. the real regex part looks like:

m<(?::[$regex_options]*)?[?/].*?[^\\][?/]>
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