Any panic: is by definition a perl bug, as perldiag says. Before reporting it, if possible see if it is still a problem with the latest maintenance release (n.b. make sure it's built with the same options before dismissing the bug as "fixed"), and if it has not already been reported. Both appear to be true in this case.

It's helpful to get the test case as short as possible. In this case: ./perl -e'qr/(?{rand < 5})/' shows the bug (but rand + 5 doesn't). Note that it happens at compile time, not run time.