The introduction oif ds_new in #738 introduced a possibility for inconsistency with ds_active -- and adding assertions that they are consistent serves to highlight those spots in which transient inconsistencies are not, in fact, incorrect. (That is, where the structures are inconsistent, but where the inconsistency has no consequence.) As @jmpesp pointed out, it would be good to rectify all of this: assert that these two structures are consistent, address those conditions in which they are inconsistent by implementation, and verify that those assertions do not diminish performance, See #738 (review) for additional details.