Of course, segfault means there is a bug. 5.022 has this in ./re/re_tests:

# Used to crash, because the last branch was ignored when the parens
# were counted:
(?|(b)|()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()(
+)()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()
+()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()(
+)()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()
+()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()(
+)()()()()()()()()()()(a))
[download]

Which is kind of similar to your example. Looks like this bug was fixed at some point, I don't know when...