See the new unittest: test/unittest/block/test_extent_list_insert_remove.cpp.
The failing test is:
TEST_CASE("Extent Lists: block_off_match", "[extent_list2]")
Three extents inserted: insert_list off=12288, size=4096; off=4096, size=4096; off=20480, 24575.
Call __block_off_match() with off=8191, size=0. It should return false. It returns true.