That suggests that the bookkeeping is going wrong for setting up the
binary-search lookup table that drives dwfl_addrsegment (segment.c).
You can probably reproduce it in an isolated test case by extracting
the sequence of dwfl_report_segment calls made in your scenario, and
then mocking up a test that does those and then a dwfl_addrsegment call
to match the bogus results seen inside this core file scenario.
Please work with Petr Machata <pmachata(a)redhat.com> to synthesize that
test case for our regression tests, and then Petr can fix the code.