https://fedorahosted.org/sssd/ticket/1947
A fast explanation how _srv_ expansion works. _srv_ is inserted into server list as so called meta server. Let us consider following configuration:
*Setup* ipa_server = _srv_, ipa.pb server list will contain: meta -> ipa.pb
*Expansion* meta -> ipa.pb:389 -> ipa.pb ; remove meta ipa.pb:389 -> ipa.pb ; meta
*Collapse* remove ipa.pb:389 ; insert meta meta -> ipa.pb
The main problem is that expanded SRV servers are marked as NEUTRAL during online check, but they don't collapse back into a meta server.
This will trigger another SRV expansion, leaving the old server in the list and trying to add the servers again. This is present in both master and 1.9 (and probably older versions), although the result is slightly different.
In master, we don't insert a server into server list if it is already present. Because state->meta is orphaned from the previous SRV expansion, state->meta->next is NULL and SSSD crashes later.
In 1.9, we simply insert duplicate servers. Those servers are inserted after orphaned state->meta, state->meta is orphaned again, leaving those servers globally unreachable. However, it seemingly does not affect the fail over. You just run into d25e7c65.
Here are four patches for master, and two patches for 1.9.