The problem is around line 3000 in sv.c; the comment there reads:

/*
 * If /x was used, we have to worry about a regex
 * ending with a comment later being embedded
 * within another regex. If so, we don't want this
 * regex's "commentization" to leak out to the
 * right part of the enclosing regex, we must cap
 * it with a newline.
 *
 * So, if /x was used, we scan backwards from the
 * end of the regex. If we find a '#' before we
 * find a newline, we need to add a newline
 * ourself. If we find a '\n' first (or if we
 * don't find '#' or '\n'), we don't need to add
 * anything.  -jfriedl
 */
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This is only a display bug -- it doesn't effect the way the regex matches.

It looks like it's not looking earlier than the # to see if the # is preceeded by a \. Unfortunately, I don't think it's just that easy, either, as qr[ \\# ] should get the newline..

perl -pe '"I lo*`+$^X$\"$]!$/"=~m%(.*)%s;$_=$1;y^`+*^e v^#$&V"+@( NO CARRIER'