I don't know why it doesn't happen for statically compiled regular expressions. Maybe this is the real bug here.
But it does: 
$ perl5180 -e'/(?<!ss)a/i'
Variable length lookbehind not implemented in regex m/(?<!ss)a/ at -e 
+line 1.
$

[download]

Dave.

In reply to Re^2: qr/STRING/ fails with certain lookbehind expressions by dave_the_m
in thread qr/STRING/ fails with certain lookbehind expressions by wiewa

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