Nasty Bug in 10.5(2) with SIP and FQDN

I recently ran into this bug as a customer who was on 10.5.2.12900-14 transitioned to a CUBE router to a SIP carrier.  As part of the process we implemented FQDN as well.  The bug is CSCuu97800.  The issue is that when CUCM is presented with a SIP call and the FQDN is in the contact of the SIP header. The CUCM has to do a DNS lookup on the FQDN.  This is causing a crash on the CCM service.

This is what the Defect indicates:
When an inbound refer or SIP dialog message happens with MeetingPlace, Exchange, or MultiNode environment), and has an FQDN in the SIP CONTACT header requiring CUCM to do a DNS lookup the CUCM CallManager service crashes/cores and all calls is disconnected. All phones are unregistered from CUCM temporarily as well.

If you are on the exact version above as this customer was there is a cop file to install that will fix the issue if you are not inclined to upgrade at this time.
The cop filename is ciscocm.FQDNwithDNS-v1.0.k3.cop.sgn and can be downloaded from the 10.5 download area on Cisco.com.  The bug is currently fixed in 10.5.2(SU2a) and above, as well as any available version of 11 and 11.5.

Here is the readme for the cop file http://www.cisco.com/web/software/282204704/18582/ciscocm.FQDNwithDNS-v1.0.k3.readme.pdf

Some symptoms that you might see.  There will be core dumps present as the CCM service is crashing and should produce a core dump.  You will see all of your phones unregister and re-register.
To see if there are any core dumps issue the cli command utils core active list and see if there is anything recent.

Of particular note.  10.5.2.12900-14 is still available on the Cisco.com site for download even though it probably shouldn't be.  Usually with a significant enough bug a version will be pulled from the site.  This one has not been and in my research I have seen people run into this bug as far back as July, 2015.  The affected versions in 11 and 11.5 are not available for download.