500 when pressing "Create pull request"

This issue surprisingly seems intermittent, but when it happens it can be constant.

When creating a basic "pull request" you'll click the form with no response ( no errors, etc ). Only when viewing the network request in a console will you find a 500.

I can provide a URL to a Bitbucket employee ( as it appears to contain sensitive information ), but the error/contents of the URL is as follows:

{"error": {"message": "duplicate key value violates unique constraint "bb_userprefs_user_id_1feb457749eed4bc_uniq"\nDETAIL: Key (user_id, key)=(1926603, close-anchor-branch) already exists.\n", "detail": " File "/opt/python/domains/bitbucket.org/current/bitbucket/local/env/lib/python2.7/site-packages/piston/resource.py", line 198, in call\n result = checked_meth(request, args, **kwargs)\n File "/opt/python/domains/bitbucket.org/current/bitbucket/local/env/lib/python2.7/site-packages/piston/resource.py", line 185, in checked_meth\n return meth(*args, **kwargs)\n File "/opt/python/domains/bitbucket.org/current/bitbucket/local/env/lib/python2.7/site-packages/newrelic-2.5.0.94/newrelic/hooks/component_piston.py", line 33, in *call\n return self._nr_wrapped(*args, **kwargs)\n File "/opt/python/domains/bitbucket.org/2013-07-26/bitbucket/../bitbucket/apps/api/v10/handlers.py", line 5242, in read\n result = taskresult.get()\n File "/opt/python/domains/bitbucket.org/current/bitbucket/local/env/lib/python2.7/site-packages/celery/result.py", line 108, in get\n interval=interval)\n File "/opt/python/domains/bitbucket.org/current/bitbucket/local/env/lib/python2.7/site-packages/celery/backends/base.py", line 185, in wait_for\n raise result\n", "id": "d677f786456a4a